Robin Williams Hologram was featured in the Season Eighteen episode "#HappyHolograms". He was modeled after the famous comedian whose tragic and shocking death happened months before this episode. He was the only celebrity hologram to only have a cameo appearance.
Robin Williams Hologram is a computer program designed by Syntec Hologram Company. It was said to perform at the Washington Redskins: Go Fuck Yourself Holiday Special, but was only seen in the opening.
The real Robin Williams was a huge fan of South Park. He performed Stone and Parker's song Blame Canada at 1999 Oscars. Ironically, the original choice to sing it, Mary Kay Bergman, the female's voice actress fell into a depression and committed suicide just like Robin.
When Robin appeared as a hologram, he wore reindeer antlers and a red Rudolph nose, which may be a reference to Patch Adams.