Check out five things you didn't know about Robin Williams!

1.  He and Christopher Reeve were the only two people in a prestigious acting program at Julliard in 1973, and they stayed friends. When that tragic horse-riding accident made Reeve a quadriplegic, Williams visited him in the hospital...

But he pretended to be a Russian doctor who was there to perform a COLONOSCOPY.  Reeve said it was the first time he'd laughed since the accident...and it helped him realize he was going to be okay.

2.  He did the Genie in "Aladdin" for 'only' $75,000, and improvised most of his lines. To the point where the Academy Awards rejected the movie for Best Adapted Screenplay, since so much of the dialogue was made up in the studio.

His performance is also credited with starting the whole 'huge celebrities doing voice work in animated movies' thing.

3.  His senior class at Redwood High School in northern California voted him both "the funniest" AND "least likely to succeed." He went on to win five Grammys, two Emmys, and an Academy Award.

4.  He was good friends with John Belushi, and obviously they partied way too much together.

And he and Robert De Niro were the last two celebrities to see Belushi alive, on separate visits to his bungalow at the Chateau Marmont Hotel in Hollywood in March of 1982.

5.  He was married three times...the first was in 1978. But he had an affair with a cocktail waitress, who sued him in 1986 for giving her herpes. So he got divorced in 1988.

The next year he married his NANNY, who was several months pregnant with his child.

6.  His big break was "Mork & Mindy", which was actually a spin-off from a season five episode of "Happy Days"...Mork tried to take Richie Cunningham back to his planet Ork as a human specimen, but was foiled by Fonzie. Seriously.

He got the gig by showing up to the "Happy Days" audition in rainbow suspenders. And when they asked him to sit down a little differently, the way an alien might, he did a headstand on the chair.

(Wikipedia / Huffington Post / IMDB)