Dio Brando/Personality and Relationships

Personality
Dio is consistently manipulative and violently domineering, and has repeatedly shown a lack of conscience and empathy.

Dio's most recognizable characteristics are his boundless ambition and his love of power. Abused by his father and having lived in the most miserable living conditions, Dio set for himself the goal of becoming the richest, then the most powerful being on earth. To do so, Dio used anything or anyone that he could use to further his goals, disregarding any kind of morality who would restrain the range of actions available to him. Using either manipulation and seduction, or plain violence, Dio constantly sought to become more and more powerful. Dio enjoys being in a position of power and has repeatedly stated how great he felt being in a dominating position. On the contrary, Dio never tolerated that someone could stand up to him or equal him in power, and was several times enraged and deeply disturbed at the thought.

Throughout his life, Dio has tended to surround himself with witless cronies and later minions, who were attracted by his natural charisma. Not thinking much of them at first, he then selected those he deemed as particularly evil, claiming that an evil person wasn't bound by rules such as honor and thus were stronger mentally. This belief culminated in including the absorption of 36 souls of sinners, or as he claims particularly strong souls, to unlock a power greater than that of The World.

Naturally, Dio is an incredibly selfish person, only looking over his own interest and overlooking those of others at best, trampling them on the ground at worst. Due to his composed nature, Dio can and will openly offer himself to any gender using any method, as long as the person suits his present desires. Since he is selfishly interested in their capabilities, however, Dio is the type who is incapable of loving another person wholeheartedly. The only persons he can be said to have held some type of affection for was his mother, Jonathan Joestar, and Enrico Pucci; Dio recognizing Jonathan's worth as equal to his own, and having been friends with Pucci. Still, Dio stole the former's body and his friendship was nonetheless merely a part of a grander plan to further himself.

Phantom Blood
"I reject my humanity! JoJo!"

- Chapter 11, to Jonathan, before wearing the Stone Mask

In Phantom Blood, Dio is ambitious, arrogant, and megalomaniacal, seemingly able to do anything to achieve his aims. His natural ruthlessness is exposed very early when he swears on his father's grave to exploit the Joestar family despite them being kind enough to adopt him. In order to place himself in a better position to replace Jonathan Joestar and obtain the Joestar family fortune, Dio used the most underhanded means to break him mentally. These methods included: humiliating Jonathan in public sport fighting, ostracizing him from his friends, and finally stealing Erin Pendleton's first kiss to drive a wedge in their budding relationship. When he is eventually foiled, Dio opted to slowly poison George Joestar I and kill Jonathan with the Stone Mask to make both deaths seem natural and accidental. Dio has shown a remarkable determination to reach his goal, never losing his drive despite the numerous defeats he suffers throughout Phantom Blood and always tried to find a way to get back at Jonathan for them.

Dio's lack of empathy is also apparent, since despite having lived for years with the kind Joestars, he never thought of them as anything more than obstacles, and is hinted to utterly resent the upper class he frequents. Dio has been maintaining a facade of a charming and agreeable person to everyone save Jonathan, yet never came close to anyone. At the end of the part, the only person Dio appreciated was Jonathan Joestar himself, begrudgingly acknowledging his valor as his archenemy and "granting" him a painless death, and was even shocked to see him die. Overjoyed to have changed into a powerful vampire, Dio spent his battles taunting various humans about their weakness and belittling them in favor of the apex predator vampires. Dio also sadistically changed a mother into a zombie just to watch her devour her own baby.

Dio shows a lack of restraint in his violence, and is prone to murderous outbursts even as far as his childhood, notably trying to stab Jonathan when he beat him up, and violently slapping Erina. He was also incredibly cruel to Jonathan's dog, Danny, going so far as kicking him on their first meeting. When Dio was defeated by Jonathan, Dio incinerated the dog. He is shown to be utterly enraged when someone stands up to him, which is the cause for his outbursts.

Dio's personality could be explained by his poor childhood and the abusive relationship he shared with his father, Dario Brando. Speedwagon, however, denied this as a cause for Dio's personality, claiming that Dio was simply born this way, and that poverty had nothing to do with it. True to that, Dio was already an immoral person but then openly relinquishes his humanity in favor of becoming a vampire upon being cornered by the police. He trades his underhanded scheming persona for a more arrogant, hedonistic, and dismissive of humanity personality that revels in his evil. Nonetheless, Dio respects determination and said much to Jonathan that his determination was equal to his own, earning him the dubious honor of serving as Dio's new host, after Dio was reduced by Jonathan to a head.

Dio's potential for empathy is emphasized in both the manga and the anime, when Dio is shown to have killed his own father out of revenge for the abuse against his mother, rather than as a step in his scheme to rise in society.

Stardust Crusaders
"Everyone survives in pursuit of peace of mind. ... Aren't you uneasy, preparing to fight me, knowing you may die? ... If you join me, I will give you peace of mind that will last forever."

- DIO to Polnareff, Chapter 248

Reappearing in Stardust Crusaders, DIO ultimately didn't change much since his burial at the bottom of the ocean for one hundred years, still being a murderous megalomaniac, but nonetheless having matured a little by recognizing valor in others and being generally more calm and levelheaded.

DIO doesn't appear much in Stardust Crusaders as a whole, but is seen discussing various philosophies with Stand users he wishes to recruit, and with his already loyal followers, particularly Enya the Hag who serves as his main adviser. It seems equally likely that DIO does this to manipulate and persuade as that he believes what he says, but nonetheless acknowledges the power and valor simple humans can have, notably respecting one's willingness to die for his goal. Wishing to quickly dispose of the Joestars, he listened to Enya and was told that she'd already sent agents to deal with them, and quietly rested in his mansion to gain more strength. Furthermore, DIO learned his lesson and stops underestimating his opponents, being particularly careful around the Joestar bloodline. He nonetheless sneered at other Stand Users' efforts to fight him, notably Kakyoin's, whose discovery ended up being crucial in his defeat.

This time, DIO is far more calm and collected. Maybe due to knowing that his Stand The World is far above anyone's reach, DIO is more tolerant of people resisting him, and didn't react to Polnareff's taunts and insults. He even seems to appreciate Hol Horse's insubordination, which confirms the mercenary's strength, and let him go try to assassinate Jotaro. However, DIO is still callous about human life and killed anyone who would fail him, even Enya - who was, again, his closest adviser. The usually confident and cunning gambler Daniel D'Arby was driven to madness when he couldn't handle the pressure of possibly revealing DIO's Stand ability to Jotaro. True to himself, DIO is enjoying the fact that he is wielding the most powerful Stand in his organization, being unconcerned by the heroes' effort to discover his power as he thinks they are meaningless. When Jotaro reveals himself to be able to move within the stopped time, DIO is initially very distraught but recomposes himself quickly, devising other plans to get rid of Jotaro by exploiting his advantage. The full scale of his insanity is visible when, overjoyed to have completely fused with Jonathan's body and being at full power, DIO declares that he was experiencing "the greatest high" and drills his index finger into his skull. His final speech exposes that he still is willing to use any way to win and despises any concept of honor or revenge, ultimately using a cheap trick to blind Jotaro momentarily.

Stone Ocean
"...Beyond the powers of my Stand is where you need to go in order to find Heaven. What you need is a trustworthy friend ... Will I, DIO, be able to meet someone like this one day?"

- DIO's Diary

In flashbacks placed before the events of Part 3, DIO demonstrates a burgeoning ability to be genuinely nice to another person in numerous conversations with Enrico Pucci. Intrigued by Pucci, who let him be despite suspiciously hiding in a church, DIO healed his crooked foot, a kind gesture, and gave him the head of an Arrow, which would grant him his own Stand, Whitesnake. During these flashbacks, DIO is seen peacefully chatting about random trivia, and confessing to Pucci that the priest could make him be at peace. Once daring Pucci to steal his Stand, to Pucci's refusal, DIO thanked him for his fidelity, and even admitted that he feared the thought of Pucci betraying him.

It is debatable how good a friend DIO truly was, considering Pucci's good-willed nature during his youth directly opposing his later evilness and zealotry. DIO also seems to have built that friendship to further his ambitions, which questions how sincere it was. It is implied that he wanted to use his Stand to create a perfect world for himself and a handful of subordinates. He enlisted Pucci as his living "conscience", in case he would go crazy and veer "off track".

Family

 * Dario Brando: Dio hated his father and saw Dario only as a stepping stone in his path to ascend in society. Dio's hatred stems from the abuse Dario dealt Dio's mother with his alcoholism, as well as Dio himself, to the point where he secretly poisoned to death and tricked Dario into thinking he was sick. He emphasizes this by spitting on his father's grave before leaving for the Joestar mansion.
 * Dio's mother: Though she isn't seen interacting with him, it's very clear that Dio loved his mother deeply, and the abuse she was dealt by his father was one of the reasons Dio slowly and painfully killed Dario.
 * Giorno Giovanna: DIO is not shown to have interacted with his son, Giorno, although Giorno keeps a photo of him in his wallet. It is unknown where Giorno got it from or if he knows of the kind of person his father was. Also of note is that DIO would drained Giorno's mother of her blood, had he not been killed himself by Jotaro.
 * Ungalo, Donatello Versus, and Rikiel: Similar to Giorno's case, the mothers of all three men were left alive. However, none of them inherited Jonathan's spirit. All three only learned their true father's identity after their fated encounter with Pucci.

Allies

 * Enrico Pucci: DIO's encounter with Pucci is presumably the most prominent example of humanity displayed by him and was his first proper friendship with another person, as he showed compassion by healing Pucci's foot when they first met. Through the time he spends with Pucci, DIO comes to trust him enough to allow Pucci to inherit control of his plan. At one point, DIO forced Pucci's hand into his head and nearly had his Stand DISC removed to test Pucci's loyalty to him.
 * Vanilla Ice: While the former is fanatically loyal to his cause, even willing to chop off his head to prove his worth, DIO annoyingly notes that Vanilla Ice often forgets about the doors after he uses his Stand, Cream, to travel via making a hole in the wall.
 * Wang Chan: While at first a provider of his secret oriental poison that was crucial in killing Dario and attempting to kill George, after becoming a vampire, Dio used him as a scout and aide once his head is chopped off. Despite his dependence on Wang Chan, Dio doesn't take his insults to Jonathan lightly and threatens him for it.
 * Petshop: While not much is known about their relationship, Dio personally selected Petshop as the guardian of his temple while he was in Egypt.
 * Enya the Hag: Enya was one of Dio's most loyal followers and supporters. Despite her loyalty, Dio secretly implanted her with a flesh bud to insure her secrecy.
 * N'Doul: Dio was the first person to see N'Doul's worth which caused N'Doul to admire Dio. N'Doul was so loyal to Dio, that he killed himself in order to prevent himself from leaking valuable information.
 * Johngalli A: While there is no on-screen interaction between them, Johngalli was highly loyal to Dio, as shown when he framed Jolyne for murder and attempted to kill her and Jotaro to avenge him.

Enemies

 * Jonathan Joestar: One of the most impactful relationships Dio ever had was with his adoptive brother, Jonathan Joestar. He initially viewed his adoptive brother as a stepping stone and pest to be driven to despair and abused in order to gain the Joestar family fortune. After being beaten once, he viewed him as more of a threat, feigning brotherly bonds in public, while secretly poisoning George Joestar in order to get his fortune quicker. He intended to kill Jonathan with the Stone Mask, but upon discovering the hidden power to unlock the vampire powers of man, he decided to use it on himself in order to become one. After another failed attempt to kill his adopted brother, due to his ego, Dio decides to have others face him rather than turn Jonathan into a zombie himself. After being bested by Jonathan, he quickly changes his mind, only to be thwarted once again. In their final confrontation, Dio admits he respects Jonathan (to the point of scolding Wang Chan for taunting him) and is genuinely shocked when Jonathan dies. Dio would later defile Johnathan's grave and use his body as a host.
 * William Anthonio Zeppeli: Due to Dio having used the Stone Mask and becoming a Vampire, Zeppeli immediately viewed Dio as an enemy once he learned about the incident at the Joestar Mansion and due to his own father using the same mask to become a Vampire himself. Dio himself is dismissive of Zeppeli's hatred towards his vampiric ways and connection to the Stone Mask, only viewing Zeppeli's mastery of the unfamiliar Ripple as nothing more than magic tricks.
 * Robert E. O. Speedwagon: After hearing from Jonathan what Dio was doing to George Joestar I, Speedwagon decided to help with finding the man that sold Dio the poison. Dio openly declares that after killing Jonathan, he would dispose of Speedwagon as well for being involved. After everything that had happened at the Joestar Mansion, Speedwagon went along with Jonathan and Zeppeli to defeat Dio, knowing that he was too dangerous now as a vampire to be left running around.
 * Dire, Straizo, and Tonpetty: Being Ripple Warriors, the three knew the dangers of the Stone Mask and viewed Dio as an enemy because of his use of it. Out of the three of them, Dire was the one who really wanted to defeat Dio on his own, due to having been a friend of Zeppeli's for many years and Dio having a role in his death. At the time, Straizo knew that defeating Dio was important; however, many years later, he would admit to the older Speedwagon that he was envious of Dio due to the fact he would never age while Straizo would. This envy became so much that he would later use the Stone Mask on himself just so he could become young again.
 * Joseph Joestar: DIO needed Joseph in order to complete the merger of his head with Jonathan's body, secretly manipulating his minions to bring him closer and closer in order to drain his blood. Joseph had heard stories of Dio from Erina when he was small and knew of the danger he would bring. His hatred for DIO intensified, however, when he learnt that he had stolen the body of his grandfather, Jonathan Joestar, to use as his own. This hatred got to the breaking point when DIO's very existence threatened the life of Joseph's daughter Holy. Figuring out that since DIO was the cause of all the Stands in the Joestar family activating, it was more than likely that killing him would save Holly. That plan in mind, Joseph, along with his grandson Jotaro, his old friend Muhammad Avdol, and new ally Noriaki Kakyoin, decide to go to Egypt where DIO had gone to hide, and kill him.
 * Noriaki Kakyoin - Having met DIO on a holiday in Egypt with his family and then put under his control with a Flesh Bud, Kakyoin was loyal to him and would do anything he wanted. However, upon having the bud removed by Jotaro and seeing the harm DIO was causing towards the innocent Holly Kujo, who had shown him kindness as he was recovering at the Kujo residence, Kakyoin decided to go with Joseph, Jotaro, and Avdol to Egypt to defeat DIO.
 * Jean Pierre Polnareff: Like Kakyoin, he too met DIO and was placed under his control. After having the Flesh Bud removed by Jotaro, Polnareff decided to join the team, though at first for his own goals, as Polnareff theorized that DIO would know where his sister's killer would be. Even after he avenged her sister's death, Polnareff chose to stay with the group to defeat DIO. After the deaths of both Avdol and Iggy, Polnareff vowed to defeat DIO no matter what.
 * Muhammad Avdol: Unlike Kakyoin and Polnareff, Avdol recognized who DIO was upon meeting him, due to having heard about DIO from Joseph. As such, Avdol knew the man was an enemy immediately and managed to escape from him before he could be put under his control. With DIO threatening Holly's life due to him activating all the Stands in the Joestar bloodline, Avdol, along with Jotaro, Joseph, and Kakyoin decided to journey to Egypt to defeat Dio.
 * Iggy: Iggy was dragged against his will into joining the Joestar Group in Egypt, and as such didn't care about DIO or what was happening, being more concerned about himself. After his fight with Pet Shop though, he decided to help the group defeat DIO, as it was because of him that Iggy was brought to Egypt and put through so much trouble in the first place. In the end, DIO and Iggy never personally encounter one another, as Iggy dies protecting Polnareff during his fight with Vanilla Ice.
 * Jotaro Kujo: DIO viewed Jotaro as much of a threat as Jonathan was, if not more, going to extremes to outwit and ensure his death. While Jonathan was an opponent DIO respected, Jotaro was an opponent DIO feared. Jotaro on the other hand, despite being able to hide his emotions from other people, was secretly worried about his mother's failing health caused by her Stand and wanted to defeat DIO as quickly as possible, as her Stand was caused by DIO activating all the Stands in the Joestar bloodline at the same time. After DIO had apparently killed his grandfather Joseph right in front of him, Jotaro's hatred for DIO intensified to where, for the first time, Jotaro was visibly enraged and acted on anger. After a long and grueling fight with the vampire, Jotaro finally managed to outwit and kill DIO.

OVER HEAVEN
(The information below derives from a Light Novel not written by Araki. As such, it may or may not be considered canon.)

JoJo's Bizarre Adventure: Over Heaven offers an interpretation of Dio Brando's character by mixing elements present in the original material and plot points introduced by the light novel. Most notably, Dio's fixation on heaven is explained as the result of the influence his dead mother had on him. In the novel, Dio is presented as having developed past his megalomaniac self and began an introspection about his life and his growth.

Relationship
Daniel J. and Telence T. D'Arby: Dio saw the Darby brothers as important tools to enter into heaven. While he believed their souls were too impure to enter themselves, he acknowledged their ability to manipulate souls as useful for his own ascension.

Enya the Hag: While the novel doesn't add too much to their relationship, Dio states that he would've considered letting her bear his child if she was younger.

Dario Brando: While their relationship is about as negative as it is in the manga, it is revealed that he hated his father for allowing him to enter the Joestar Mansion because he thought that one act of kindness allowed Dario to get into heaven and one of the reason he wanted to get into heaven was to kill his father again.

Dio's Mother: In the novel it is revealed that his mother taught him everything he knew about the world. While Dio is unsure if heaven really exists, he believes that her death saved her from her living hell of a life. It is revealed that the words in his diary are from a nursery song she sung him.

Unborn Sibling: It is revealed that Dio's mother was pregnant with an unborn sibling but ended up miscarrying him/her.

Erina Pendleton: Dio respects Erina's strength and in someways saw her a bigger threat than Jonathan. DIO theorizes that Erina Joestar placed both him, herself, and the infant Lisa-Lisa in the casket on the boat where Jonathan died in order to escape the boat's explosion. DIO at first believes that Erina did this in hope DIO may return some day as a better man with Jonathan's body. He quickly dismisses the idea, stating that if it was the case that Erina reminded him of his mother.