Him and Marlon Brando
Similar in that eventually they stopped caring about film.
Brando at least was open about his disdain for acting, he basically stopped caring after Last Tango In Paris (1973) and 'I've had enough, I just want the money' then started doing films that were beneath him, He did do the occasional good film however.
De Niro is basically the same but he doesnt admit it, He just does these awful films, it is almost painful seeing maybe the greatest actor of all time demean himself by doing these crap films, Brando did Island Of Dr Moreau (1996) but it was a masterpiece compared to some De Niro films.
However in later years both did some good films
Brando
A Dry White Season (1989)
The Freshman (1990)
Don Juan Demarco (1994)
The Score (2001)
De Niro
The Good Shepherd (2006)
Silver Linings Playbook (2012)
The Intern (2015)