The Big Bang Theory has been TV's greatest home to geekdom's favourite guest stars – but the biggest of them all has turned them down, with William Shatner opting not to appear.

Many Star Trek legends have appeared alongside Sheldon, Leonard and co in the CBS sitcom, including Leonard Nimoy, Brent Spiner, Levar Burton, George Takei, and the ubiquitous Wil Wheaton.

But there's been one Starship Enterprise great that is sorely missing from that list: William Shatner, the original Captain James T Kirk, who has yet to boldly go where other Star Trek faces have gone before.

It turns out that Shatner has been offered a role in the show, but he declined the offer as he wasn't content with the script. The good news is he hasn't ruled out a future appearance on the hugely successful sitcom.

He told Digital Spy: "I've had several conversations with the creators, and what they wanted me to do, didn't seem to be exactly right, so I said 'Find something that's better'. They may have taken umbrage at that, I'm not sure."

Explaining what was originally on offer, he said: "They wanted me to play myself a little obliquely, and they said it would work out, but I needed more assurance on that."

The Big Bang Theory returns to RTÉ2 later this autumn.

Here's Leonard Nimoy's cameo on The Big Bang Theory:

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