Slightly less frequently seen in Coppola’s epic tale of two Dons in “The Godfather Part II,” Duvall’s German-Irish lawyer still earns his spot at the Corleone desk and is a welcome addition whenever he’s on screen. Helping Michael get out of an impasse with his Senate hearing in Washington and secure Frank Pentangeli’s silence, he’s not only a respected and trusted confidant to the new family owner but He’s also a character with his own story. It thus raises the question of why Michael’s devoted second-in-command was killed off-screen between “Part II” and “Part III”. Doesn’t the person who helped the new godfather keep the Corleone family in power deserves a little more respect? Well, as revealed by the actor himself, he doesn’t feel like he’s got anything.
In the third and least beloved film of the trilogy, Tom’s absence is reasonably quickly explained, with Michael mentioning that the family attorney died at some point in the film. 20 years gap between “Part II” and “Part III”. While the cause of death has never been confirmed, Michael still mourns his old friend and respectfully helps his son, Andrew Hagen, who has been ordained a priest, obtain a high position at the Vatican. However, the truth is that Tom was written out of “The Godfather Part III” because Duvall refused to return.
https://www.looper.com/662127/the-real-reason-tom-hagen-died-before-the-godfather-part-iii/ | The Real Reason Why Tom Hagen Died Before The Godfather: Part III