The four-hour documentary about him directed by Peter Bagdanovich is currently available on Netflix and well worth the time.
One part of that doc that was kind of humorous but really showed Tom's personality was when he was in the studio to help with a Roger McGuinn album. He was listening to the songs that were going on the album and reading the lyrics when he smelled something fishy. The producer or producer's friend (been a while since I've seen it) was trying to sneak one of his own songs on the album. Tom says to the producer, "What is this s*? Did you write this s*? and then tore the guy a new one for trying to sneak one of his own crappy songs on Roger's album. He was a fighter and a standup guy and seemed like a great friend to have.