Professor Hulk was first said to be a combination of Banner and two different versions of The Incredible Hulk, Savage Hulk and Grey Hulk.
The artwork in question seems to indicate that fans may be seeing Professor Hulk in Avengers 4, although that has yet to be confirmed.
It was later revealed that Professor Hulk was actually a fourth different “personality,” which represented the “ideal” version of Hulk.
Perhaps the most intriguing detail, though, is a much different Hulk, smaller than his previous incarnations, leading many to speculate that Professor Hulk will surface.