I had to google it. Apparently Jeff Corwin hosted a tv series about the Georgia Aquarium called Ocean Mysteries. I'm not sure how that translates to it being "most famous".I grew up on Steve Irwin and Jeff Corwin, I'd never heard of Jack Hanna until around the time I joined this forum. Even then, I never associated Irwin with the Australia Zoo and until this very moment I did not know Corwin was associated with Georgia Aquarium.
I have heard of Jeff Corwin - wouldn't be able to tell you anything about him though. I wouldn't even be able to identify him from a line of mugshots. I think you'd be hard-pressed to find (non-Zoochat) people outside the USA (and outside of a certain age) who have heard of either Jeff Corwin or Jack Hanna. I suspect even the city of Columbus is pretty unknown outside of the USA, let alone its zoo.
Steve Irwin is obviously still world-famous but only as "the Crocodile Hunter" - I'd wager that relatively few people associate him with Australia Zoo because he is largely famous for his persona.