However, to me, his signature role will always be the title role of Brian Piccolo Brian's Song (1971) with Billie Dee Williams as Gayle Sayers, one of the few movies where it is OK for guys to cry. That movie and that role is what I always remember about Caan first though you can't forget Rollerball (1975) either.
P.S. In 1986 and 1987, signature Vietnam movies Platoon (1986) and Full Metal Jacket (1987) came out. Great movies, but another, lessor heralded movie in that genre came out Gardens of Stone (1987). Caan was the star of that movie, directed by Francis Ford Coppola, which also had in it Anjelica Huston, James Earl Jones, D. B. Sweeney, Dean Stockwell and Mary Stuart Masterson. If you haven't seen that one, you want too. Acting, dialogue, and what some in the military had to go through on the home front.