Personality
As a young man, Joseph was incredibly hotheaded, impetuous, and confrontational. He was not very serious or focused and tended to fool around, but was shown to be incredibly savvy. At crucial points in battles, he will verbally predict what will happen to his enemies in a Fist of the North Star-like fashion, and quote, often verbatim, what they will say. His enemy will then unwittingly repeat said prediction, shocked by Joseph's "mind reading". This is primarily prominent in Part 2, although he does perform this feat again in Part 3 just before he destroys The Empress. Over the course of Part 2, although he never really lost his overall attitude, he did develop into a strong, focused hero. It is revealed in flashbacks that Joseph collects comics and was a fan of Superman when he was young. He becomes a fan of Rohan Kishibe's works when he is much older.
In Part 3, Joseph is much the same, only as an irascible old man with a temper and the same mischievous spirit as in his younger days. He is, however, much more easily surprised than he was in his youth. Being older, he is certainly more mature and serious. He and Jotaro, despite their hostility at first sight, manage to communicate with one another mentally. He is also able to offer advice to his hot-headed grandson and becomes a father figure to Jotaro over the course of the story.
In Part 4, his advancing age has weakened his mind and he appears to have become somewhat senile. He is not nearly as confrontational as he was in his youth, even sadly accepting Josuke's demand that he not interact with Josuke's mother. He also appears to have lost some of his prior cleverness, as he is easily taken in by a salesman when buying baby utilities and ends up spending about $1,000 (shown to be about 135,000 Yen). Despite all his failures, however, he has become a well-meaning old man who is still willing to risk his life for others.
Relationships
Family
- Suzie Q Joestar: Joseph is shown to have expressed some attraction towards Suzie Q upon seeing her early on in Part II, though does show some degree of exasperation at her airheaded demeanor when he realizes that she had not sent a telegram bearing news that he was living to his family and friends. Fifty years later into the marriage, Suzie Q is shown to trust her husband completely and believes that he had never failed her once, but expresses utter rage when he reveals that he had a secret child with another woman. This rage is mentioned again when he brings home an adopted daughter named Shizuka, who Suzie Q believes to be another illegitimate child.
- Jotaro Kujo: Initially, Joseph is shown to have a rocky relationship with his grandson, angrily demanding that he exit his cell, and is forced to have Abdul unleash his stand instead after his finger on his prosthetic hand is ripped off. Shortly after, he places his trust in his grandson when he removes Dio's flesh bud from Kakyoin's head. Later throughout the course of the series, he and Jotaro are able to get along more easily, to the point where they work together to defeat Terence T. D'Arby in Dio's mansion. At the end of Part IV, he confides more in Jotaro, sharing with him his observation of the spirit and will of the residents of Morioh.