Billionaire Elon Musk, who is celebrating his 51st birthday today has been the centre of many conspiracy theories, with some even claiming he is not a human but an alien instead.

Musk, a space fanatic, has never even attempted to disprove these ludicrous hypotheses. Once, he even jokingly confessed that he, indeed, was a member of the alien species.

Last year, a Twitter page called "Tesla Owners of Silicon Valley" asked Elon Musk whether he is an alien. To which he responded by saying, "Aliens exist in Physics and Philosophy."

"Aliens could be among us...some people think I am an alien," he then added. This is not the first time that Musk has admitted to being an alien as a joke.

In one instance, an Indian entrepreneur tweeted: "Elon Musk may end up running 4+ 500 billion companies simultaneously at a relatively young age. What I want to really understand: how does he do it? How does he manage context switching? How does he design his Org? So many questions." Musk then answered: "I'm an alien."

In another instance, Musk tweeted, "The Earth is not flat, it's a hollow globe & Donkey King lives there!" When another user asked Musk if he was an alien, Musk responded with a simple "Obv." A Facebook user even went on to claim that Musk as not just an alien but an alien lizard. He added that Musk was a lizard from Mars.

Musk may have joked about being an alien during his light-hearted encounters with Twitter followers, but he admits that he has not come across any evidence that would point to the existence of life elsewhere in the universe, per a report in The Independent.

The billionaire is a frequent Twitter user, regularly mixing in inflammatory and controversial statements about issues or other public figures with remarks that are both whimsical or business-focused.

He has also sparred repeatedly with federal securities regulators, who cracked down on his social media use after a purported effort to take Tesla private in 2018 fell apart.

Elon Musk
Tesla CEO Elon Musk. Photo: AFP / Frederic J. BROWN