“20th Century Boy” is a song by T. Rex, written by Marc Bolan. It was released as a single in 1973 and reached No. 3 in the UK Singles Chart. The song was not featured on an original studio album but was included as a bonus track on a reissue of 1973 album Tanx.

It later returned to the UK Top 20 in 1991, peaking at No. 13, fourteen years after Bolan’s death, when it was used in a Chris Hartwill-directed commercial for Levi’s starring Brad Pitt. It plays a key role on the science fiction-mystery manga 20th Century Boys.