He's been called a round-headed buffoon, and mocked for years by both Ricky Gervais and Stephen Merchant, but he's also one of their nearest and dearest friends. American television audiences first discovered Karl Pilkington as the lesser known of the three leads on HBO's animated "The Ricky Gervais Show." Then came "An Idiot Abroad," which put Pilkington front and center.

But that show was as much about Gervais and Merchant torturing the man than creating an entertaining travel show. Perhaps that's why David Letterman demanded that Gervais leave him alone on "Late Show" (Weeknights, 11:35 p.m. ET on CBS). It's so hard to tell if Pilkington is in on the joke, genuinely enjoys getting teased and poked by the comedy duo, or is as frustrated as he appears most times.

Gervais is adamant that he loves Pilkington, though as much for his crazy responses and thoughts about the world than anything else. "The Ricky Gervais Show" is framed as a show to spotlight Pilkington's unique world view, and Gervais was more than happy to share a few stories emphasizing that with Letterman and his audience.

The truth about the giant squid. Karl's response: "Who's been lying about it up 'til now?" The gifts of the wise men at Jesus' birth. Karl's response: "Were them presents for his birthday or Christmas?" The 1.4% genetic difference between humans and chipmanzees. Karl: "That's gotta be the a**." You can't write this stuff, which is why Karl unscripted makes for such great radio and television.

Karl Pilkington returns with "The Ricky Gervais Show" on Friday April, 20 at 9 p.m. ET on HBO. "Late Show" airs weeknights at 11:35 p.m. ET on CBS.

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