The man from Josuke's memories is a tertiary unnamed character from JoJolion whose face Josuke briefly remembers when fighting Ojiro Sasame and assumes to be someone he knew in his past life. His identity was not revealed during the part.
History
Background
Although almost nothing is known about him, it can be assumed he met either Yoshikage Kira or Josefumi Kujo at least once since Josuke claims him to be someone he knew in his past life.
JoJolion
While fighting Ojiro Sasame Josuke briefly remembers his face.