godfather 2

Yes, he was.

Big time.

He played the young Vito Corleone...a massive role.

http://www.imdb.com/title/tt0071562/

I remember him playing a major role in the first godfather, but why would he be in godfather two, Vito Corleone was played by Marlon Brando in that flick

did you read http://www.imdb.com/title/tt0071562/ yet?

De Niro was in the flashback playing the part of Don Vito Corleone (who was played by Marlon Brando in Godfather 1) before the plot turned to Al Pacino as Michael Corleone, the new godfather of the family. In my opinion, Godfather 1 and 2 were superb. Godfather 3 not so much.