"Before we get into the show, we, like all of you, were shaken up a bit last night when we learned that genius comedian and actor Robin Williams passed away. He's one of a kind. He's one in a million. He's unbelievable," Fallon said, choking back tears, before doing his best impersonation of the legend.
"And you'd watch him and you would cry laughing and you would think I am never going to see anyone like this human ever. It's just amazing," the host continued. "His brain was always thinking 10 steps ahead of what he was saying. He was like the Muhammad Ali of comedy."
Fallon then aired a clip of Williams' first Tonight Showappearance with Johnny Carson, before standing on his desk and quoting the famous Walt Whitman poem in tribute to Williams' early film Dead Poets Society.
Watch the full tribute: