Dinosaur Jr. is an American rock band formed in Amherst, Massachusetts in 1984, originally called simply Dinosaur until legal issues forced a change in name.

The band was founded by J Mascis (guitar, vocals, primary songwriter), Lou Barlow (bass, vocals), and Murph (drums). After three albums on independent labels earned the band a reputation as one of the formative influences on American alternative rock, creative tension led to Mascis firing Barlow, who later formed Sebadoh and Folk Implosion. His replacement, Mike Johnson came aboard for three major-label albums. Murph eventually quit, with Mascis taking over drum duties on the band's albums before the group disbanded in 1997. The original lineup reformed in 2005, releasing three albums thereafter.