[PaulD]

Originally Posted by Nosferatu@Cult Labs

From Wikipedia:

The Canadian alternative rock band Barenaked Ladies wrote and recorded the show's theme song, which describes the history and formation of the universe and the Earth. Ed Robertson, lead singer and guitarist in the band, was asked by Lorre and Prady to write a theme song for the show after the producers attended one of the band's concerts in Los Angeles. By coincidence, Robertson had recently read Simon Singh's book Big Bang,[24][25] and at the concert, he improvised a freestyle rap about the origins of the universe.[citation needed] Lorre and Prady phoned Robertson shortly thereafter and asked him to write the theme song. Having been asked to write songs for other films and shows only to have them rejected in favor of other artists' songs, Robertson agreed to write the theme only after learning that Lorre and Prady had not asked anyone else.

yeah, I edited my post after googling and finding that out