AFI #089 Pat O'Brien as Knute Rockne from Knute Rockne, All American (1940)

Now I'm going to tell you something I've kept to myself for years. None of you ever knew George Gipper. He was long before your time, but you all know what a tradition he is at Notre Dame. And the last thing he said to me, "Rock," he said, "sometime when the team is up against it and the breaks are beating the boys, tell 'em to go out there with all they got and win just one for the Gipper. I don't know where I'll be then, Rock," he said, "but I'll know about it and I'll be happy."

- Pat O'Brien as Knute Rockne from Knute Rockne, All American (1940)

The bolded portion of this quote is ranked #89 in the American Film Institute's list of the top 100 movie quotations in American cinema.