'Big Bang Theory' has had already featured star-powered geeks from "Star Trek" actor Leonard Nimoy to world renowned physicist Stephen Hawking, and in February 19's episode, Nathan Fillion is set to cameo. He will play himself in a restaurant where Raj (Kunal Nayyar) and Leonard (Johnny Galecki) debates if he really is Hawking or not. And later they will recognize him and ask for a picture.

Fillion formerly starred as Captain Malcolm Reynolds in the cult sci-fi show "Firefly," which aired on FOX from 2002 to 2003. According to Entertainment Weekly, Sheldon (Jim Parsons) is a huge fan of the show and frequently express his grief for its premature cancellation. It is also no secret on the show that the cast of characters are huge fans of the short-lived sci-fi show.

Moreover, Fillion is also not the first "Firefly" cast member to join the show. Summer Glau also made a cameo on Big Bang as herself who played the traumatized genius River Tam in season two 2009.

Last week, fans have also seen the "Big Bang" guest Stephen Hawking. He played the Internet bully who criticized repeatedly for the gang of "crackpot wannabe theoreticians" and "two clowns with their heads in a bucket."

According to Variety, executive producer Steve Molaro said they decided to get Hawking back on the show in the writers' room. "We love that Professor Hawking is a part of the 'Big Bang' family," he said. "He has a terrific sense of humor, and we thought he'd be the last person you'd expect to be playing an Internet bully."

It was also learned that Hawking's scenes were shot from his home in England, but Molaro says, "He's welcome to visit our set again anytime."

The timing of the episode just before the Academy Awards is just a "happy coincidence," says Molaro. "But if it makes us look brilliant, then yes, (it's) absolutely intentional."

 'The Big Bang Theory' airs on Thursdays at 8 p.m. on CBS.