Edward Norton As The Hulk, Replaced By Mark Ruffalo
Sometimes, even an A-list actor is not worth keeping around. While Mark Ruffalo might be the face of the modern Hulk, Edward Norton was the second to play it in the 21st century. Luckily, the Hulk got recast when Marvel started to look for a more group-friendly face. In their crosshairs came Ruffalo, the original first choice for Hulk.
Also, how would anyone be able to tell when some background character in GoT was replaced? There were a ton of them, and they all looked the same.