Iron Man
Some people live and breathe Marvel universe trivia, but did you know about this casting change? Terrence Howard was replaced by Don Cheadle in Iron Man 2, promptly being kicked out of the comic book world for good. Howard's $8 million pay increase was cut to only $1 million, with the remainder of that money being given to Robert Downey Jr. It just came down to budget cuts, unfortunately for Howard.
The Amazing Spiderman
This one shouldn't be too shocking since the role of Spider-Man has already changed four different times. However, likely the most successful progression has been the switch from Andrew Garfield to Tom Holland. Garfield had aged out of the role by the time a new script came around, not to mention many found his interpretation of Peter Parker to be pretty boring. Thankfully, critics loved Holland's portrayal!