Compliments of IMDB, here are some things most people didn't know about Robin Williams:

He was a very overweight child. As a result, nobody would play with him. He started talking in different voices to keep himself company.

During the making of "Mork & Mindy", Williams departed from the scripts and ad-libbed so many times and so well, that the producers stop trying to make him stick to the script and deliberately left gaps in the later scripts leaving only "Mork can go off here" in those places so Robin could improvise.

He studied at Julliard with actor Christopher Reeve. The two remained good friends until Reeve's death in 2004.

One week after Christopher Reeve's tragic horse riding accident, Robin visited him in the hospital. However, he was dressed from head to toe in scrubs, spoke with a Russian accent, and had a surgical mask on. He was acting as if he was a real doctor and did a bunch of wacky antics. After he took off his mask, Reeve stated that, "That was the first time he laughed since the accident!".

In 1996 he reached a unique milestone by having two of his films reach the $100-million mark in the United States exactly the same week: "Jumanji" and "The Birdcage".