I never met Donald O'Connor and have no anecdotes about him that I didn't pick up in books, but I always thought he was a class act in everything he did. The "Make 'Em Laugh" number in Singin' in the Rain may be my favorite movie musical number — and that's no small achievement, doing the best song-and-dance spot in a movie starring Gene Kelly. He also held his own when he played the title role in The Buster Keaton Story. It was a dreadful, appallingly-fictionalized version of Keaton's life but he probably "did" Keaton as well as anyone could who was not Buster Keaton.
There was just something so darned likeable about O'Connor, even in his weaker films. That was, unfortunately, most of them…but somehow, he was always good. Even when they didn't let him dance, even when they made him work with the Talking Mule. I guess that explains why the man worked for sixty years. Here's a link to a pretty good New York Times obit.