Mark Zuckerberg would like you to know he is not a shape-shifting lizard person bent on world domination.

The billionaire chief executive of Facebook hosted his first Q-and-A town hall using the social network's live video-streaming program to field questions from users. Jerry Seinfeld blew in for a brief cameo and talked about breakfast foods. Amid queries about Facebook's artificial intelligence and Zuckerberg's entrepreneurship, someone wanted to know whether the 32-year-old was actually a reptile disguised as a human.

"Mark, are the allegations true that you're secretly a lizard?" Zuckerberg read aloud. "I'm gonna have to go with 'no' on that."

He added: "I am not a lizard." The Facebook founder paused to lick his lips.

Zuckerberg called it a "very silly" question and moved on to less silly things, such as techno-telepathic thought sharing. It may be a frivolous thing when a celebrity is asked to publicly deny a secret slithery lineage, but the scenario is not without precedent. In 2011, for instance, former defense secretary Donald Rumsfeld repeatedly refused to acknowledge comedian Louis C.K. on a radio show, as he pestered Rumsfeld about being a "flesh-eating" lizard alien. Three years later, New Zealand's prime minister, John Key, was forced to tackle the scenario head-on after an Auckland citizen filed an official Information Act request.

"To the best of my knowledge, no. Having been asked that question directly, I've taken the unusual step of not only seeing a doctor but a vet, and both have confirmed I'm not a reptile," Key said, according to New Zealand's Newshub. "So I'm certainly not a reptile. I've never been in a spaceship, never been in outer space, and my tongue's not overly long either."

Before it became a waggish pastime to ask prominent figures whether they are lizard people in human skin, humanoid reptilians remained firmly in the domain of science fiction and fantasy. Kull the Conqueror fought serpent-headed men in a 1929 short story by American author Robert E. Howard (of Conan the Barbarian fame). Snarling reptilian humanoids had bit parts in "Star Wars," "Star Trek," "Doctor Who" and other sci-fi staples. In 1983 when shape-shifting reptilian aliens got their first big break in U.S. network TV, it was via earthly invasion in the NBC miniseries "V."

But bridging the gap between actors in scaly makeup and a stranger asking Zuckerberg whether he is an alien would require a cultural boost from U.K. conspiracy theorist David Icke.

Icke was a promising soccer player-turned-BBC sports correspondent before he achieved fame for his reptoid hypothesis. A strange interview in 1991 with chat show host Terry Wogan launched Icke's career as one of the world's foremost conspiracy theorists when the BBC correspondent proclaimed himself the son of God. Eight years later — into a pop-culture environment primed by "Men in Black" and "The X-Files" — Icke published "The Biggest Secret," a theorist bible that has gone through half-a-dozen new printings in the years since.

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As a pair of philosophers wrote in the journal Utopian Studies in 2005, "Icke's greatest strength is not so much as an innovator of any particular strain of alien or conspiracy theory but rather in his totalizing ambition to weave numerous sub-theories into an extraordinary narrative that is both all-inclusive and all-accounting."

In "The Biggest Secret" and subsequent books, Icke claims that prehistoric aliens — the Anunnaki (possibly related to children of the Mesopotamian god Anu) — created human beings as well as a ruling class of reptilian hybrids. The lizards' descendants include the Illuminati, George Washington, Princess Diana and other British royals, George W. Bush, and numerous infiltrators among the media, the United Nations and the Trilateral Commission.

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Given the outlandishness and New World Order scope of the claims, some critics have had difficulty accepting that Icke himself believes his own writing; he has been accused of using "reptiles" as an anti-Semitic code word. But when journalist Jon Ronson asked Icke to clarify his comments, Icke stuck to his extraterrestrial guns. In Ronson's 2001 book, "Them: Adventures With Extremists," the conspiracy theorist argues: "I'm not talking about one earth race, Jewish or non-Jewish. I'm talking about a genetic network that operates through all races, this bloodline being a fusion of human and reptilian genes."

Since "The Biggest Secret," reptilian overlord epithets have bubbled up into the political sphere with increasing frequency, if mostly for comedic effect. During the 2003 Ontario elections, the campaign for incumbent Ernie Eves issued a news release describing Liberal Party opponent Dalton McGuinty as "an evil reptilian kitten-eater from another planet."  (In a subsequent radio interview, the then newly elected McGuinty gets the last laugh: "That's Premier Evil Reptilian Kitten-Eater From Another Planet, thank you very much," he said.)

By March 2013, National Security Council spokeswoman Caitlin Hayden was fielding cheeky questions from Wired magazine about a potential reptile bodyguard seen near President Obama in a YouTube video. "I can't confirm the claims made in this video, but any alleged program to guard the president with aliens or robots would likely have to be scaled back or eliminated in the sequester," she told Wired. (As far as actual belief in reptilian overlords, Public Policy Polling — which has come under fire for suspect methodology — argued that 12 million people in the United States subscribed to the theory in April 2013.)

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Outside network TV — the "V" franchise was revived twice after the early '80s debut — lizard people remain a tough sell. In October, University of Miami political scientist and conspiracy theory expert Joseph Uscinski was reluctant to dismiss any plots outright when asked by the Atlantic magazine. But one area where the academic felt confident to express his lack of confidence? Scaly alien masters.

"I think there's a less than 1 percent chance," Uscinski said, "that we're ruled by reptilian overlords."