What planet is Mork from in "Mork & Mindy"?

The answer is: Ork

Mork came from the planet Ork, and finding the right actor to play him was a cosmic comedy of errors. Trying to fit an alien into "Happy Days" wasn't exactly the easiest task. Roger Rees was cast to play the extraterrestrial visitor but got one look at the script and bolted faster than a UFO hitting warp speed. During the scramble to recast, a young Robin Williams was recommended. When the producers asked him to take a seat, Williams promptly sat on his head. They hired him on the spot.

That upside-down moment set the tone for everything that followed. Williams's lightning-quick improvisation turned Mork from a standard alien visitor into a rainbow-suspendered force of chaos. His version of an Orkan drank through his finger, slept standing on his head, and had the crew in stitches with his alien observations of Earth life.

The character was so magnetic that "Happy Days" creator Garry Marshall spun him off into "Mork & Mindy" only four days later. The show let Williams cut loose with Orkan weirdness, from aging backward to those infamous reports to his superior Orson. "Na-nu Na-nu" swept across America like alien fever, with everyone from kids to grandparents copying Mork's signature greeting and hand gesture.