Robin was an incredible actor and extremely talented at doing voices and impressions. His hilarious antics on-screen could make anyone laugh. Off screen he struggled with depression, which is ultimately what led to his death since he ended his life by hanging himself. I don't know what it's like to suffer with depression on an ongoing basis, but I've heard it's terrible. I know what it's like to feel sad, though, and the thought of waking up every morning knowing that you're going to be plagued with bleak, hopeless feelings would make for a miserable existence.
Robin served on the board for the Christopher and Dana Reeve Foundation for several years, and would do several fundraising events each year to raise money for spinal cord injury research. The CEO of the foundation said that many celebrities he'd worked with had requirements for cars and who they would talk to, but Robin would show up on his own and talked to everybody. He was also very generous and quietly donated a lot of his own money to the foundation.