Late to the party.  Everyone who said "Wolverine" pretty much left me with nothing but ditto.  Same for Superman, although I will mention that the idea that Clark Kent had a secret identity is just the right approach that no one else made stand out for me before.

And Namor?  I thought he was just an a-hole for years.  I wouldn't read an issue if he was in it!  But when Namor came out, I was hooked and the comic became a big favorite.  The idea that he was between worlds, that he had an intractable grudge against us surface-dwellers - it was all there, from his very first appearance, but it took John Byrne to distill it into something dummy me could appreciate.  The half-naked jerk who liked to shout "Imperius Rex!" all the time became the noble, tragic hero that I couldn't see before.

I would add Jahf in Elsewhen. A chill little powerhouse who we see both as a mindless engine of destruction, and as a very cool and thoughtful houseguest at the X-Mansion. A lot of depth you wouldn't expect from a random space hero.

I WISH JB had done more with the Monster Hunters! That little taste he gave us in M:TLG was enough to whet my appetite.