9. Tom Hagen - The Godfather Part III
Tom Hagen (Robert Duvall) appeared in the first two Godfather movies as the consigliere and lawyer for the Corleone crime family, typically serving as a voice of reason during fraught situations.
His cunning allowed the Corleones to survive some close calls, and if a smart, cool-headed individual was ever needed to help resolve a situation, there was nobody better-suited in the family's employ.
Tom Hagen is one of the series' most iconic characters in large part thanks to Robert Duvall's terrific performance, which in the original film netted him a Best Supporting Actor Oscar nomination.
Sadly when Francis Ford Coppola was prepping the belated sequel The Godfather Part III, however, Duvall had a salary dispute with the producers and opted not to return, causing a planned narrative centered around Tom feuding with Michael Corleone (Al Pacino) to be scrapped.
Instead, Coppola had Hagen die off-screen and effectively replaced him with a new lawyer character, B. J. Harrison (George Hamilton).
In addition to Part III's many other problems, most fans felt that the threequel desperately wanted for Hagen's presence, and the rather charisma-devoid Harrison was an unfortunately transparent, unremarkable substitute.