Same character, at least. In the same way Supergirl's Superman is the same as the guy in Batman V Superman, or Gotham's Bruce Wayne is the same guy putting together the Justice League.In other words, there's no difference.
They're the same guy.
I just finished reading Asimov's The End of Eternity, so I think of them as alternate reality analogues of the same person. That terminology just works for me.