"Get It On" (known as "Bang a Gong" in the United States) is from the album Electric Warrior (1971), the record that propelled T. Rex to glam rock stardom.
The song's famous 1971 Top of the Pops performance featured a special guest appearance by Elton John at the piano (miming, as was common on the show), combining Marc Bolan's glitter-covered look with Elton's charismatic stage presence. Released as a single, the song reached No. 1 in the UK and became an international hit. The performance helped popularize the glam rock aesthetic on British television.