By Ariana Bacle
August 13, 2014 at 11:47 AM EDT

Tuesday’s episode of The Tonight Show started not with a “hello,” but with a “nanu nanu” from The Roots’ Questlove. The drummer was paying tribute to Robin Williams, who died Monday at 63: “Nanu nanu” was how Mork said goodbye to his fellow aliens in ’70s sitcom Mork and Mindy, the show that gave Williams his start.

Later on in the show, host Jimmy Fallon sat down at his desk and held back tears as he remembered Williams. “He was one of a kind, he was unbelievable,” Fallon said. “If you don’t know his standup, you should watch it right now.” He got up and started impersonating Williams, adopting his signature voice and frantic movements. “You’d watch him and you would cry laughing, and you would think, ‘I’m never going to see anyone like this human ever.'”

After dubbing Williams the “Muhammad Ali of comedy,” Fallon queued up a clip of his first appearance on The Tonight Show in 1981, which showcased the comedian’s specific humor: In the clip, Williams jumped out of his seat and interacted with the audience, later dancing around in front of a camera and saying with boyish excitement, “Let’s make the cameraman mad now!”

When the clip ended, Fallon stood on top of his desk in an ode to Dead Poets Society“O captain, my captain,” Fallon said. “You will be missed.”

Later in the evening, Fallon’s network-mate Seth Meyers also took a moment to remember Williams on Late Night. “The saddest part of this was Robin was battling depression. If there’s anything we can do to honor his memory, I would hope it would be to use this opportunity to educate us more about this terrible affliction,” he said, adding, “We miss Robin, but we’re also very lucky to have had him at all.”