This week and next, fans of "The Big Bang Theory" are in for a treat, when geek/nerd icons Leonard Nimoy and Stephen Hawking will appear as guest stars.

This week, the long sought after guest star Leonard Nimoy will appear on the episode titled "The Transporter Manfuction", as the voice of a mint condition Spock action figure that begins to talk to Sheldon after he takes it out of the package.

In its 5th season, the makers of "The Big Bang Theory" have been trying to years to get Leonard Nimoy, who is semi-retired from on-camera work, to appear on the show.  Nimoy has long been refereced on the show by Sheldon, refering to his framed restraining order from Nimoy, being part of "Rock, Paper, Scissors, Lizzard, Spock", and a classic scene from the second season that won Jim Parsons his first Emmy award.

Co-creator Chuck Lorre said that moment is one of his favorite moments in the history of the series,

“[Sheldon] was so overcome with affection for her, he physically hugged her, which he can’t do as a character. We all stood there on the stage and everybody got all fablungent and weepy. It was a moment that rose above the show and became something else.”

After the popularity of that scene among fans, getting Nimoy to guest star was almost a necessity at that point.  Though Nimoy only appears as the voice of his action figure, he was on set with the cast whom he spoke very highly of,

"I thoroughly enjoyed myself. [They're] a talented company and a smart show; they made me welcome."

Nimoy isn't the first "Star Trek" alumni to appear on the series, Wil Wheaton has been a regular guest star, playing a fictionalized version of himself who was Sheldon's arch nemisis.  "Star Trek: The Next Generation" stars Brent Spiner and Levaar Burton have also made cameo appearances as themselves.

For most series, a guest star of this caliber would be the icing on the cake for the season, but "The Big Bang Theory" is not stopping there, bringing in famous physicist Stephen Hawking for the follwing week's episode titled "The Hawking Excitation", in which Sheldon will do anything to meet Hawking when he finds out Howard will have an opportunity to work with Hawking.  Co-creator Bill Prady calls Hawking a dream guest for the series,

"When people would ask us who a 'dream guest star' for the show would be, we would always joke and say Stephen Hawking -- knowing that it was a long shot of astronomical proportions. In fact, we’re not exactly sure how we got him. It’s the kind of mystery that could only be understood by, say, a Stephen Hawking."

Like Nimoy, Hawking has been a source of jokes for the series with Leonard reciting a joke of Stephen Hawking participating in phone sex, and Howard referencing Hawking in the series premiere.

Hawking, who is confined to a wheelchair due to a motor neurone disease related to amyotrophic lateral and sclerosis and must use a computer controlled voice box, is also known for having a great sense of humor, appearing as "himself" in "The Simpsons", "Futurama", "Star Trek: The Next Generation", and participating in sketches for "Late Night with Conan O'Brian".

Leonard Nimoy's episode airs this Thursday, with Stephen Hawking's episode set to air next Thursday, April 5th.