Dream Theater is an American progressive metal band formed in 1985 under the name Majesty by John Petrucci, John Myung and Mike Portnoy while they attended Berklee College of Music in Boston, Massachusetts. They subsequently dropped out of their studies to concentrate further on the band that would eventually become Dream Theater. Though a number of lineup changes followed, the three original members remained together until September 8, 2010, when Portnoy left the band and he was replaced several months later by Mike Mangini. James LaBrie has been the lead singer of Dream Theater since 1991, replacing Charlie Dominici who had left the band two years earlier. Dream Theater's first keyboardist, Kevin Moore, left the band after three albums and was replaced by Derek Sherinian in 1995 after a period of touring. After one album with Sherinian, the band replaced him with current keyboardist Jordan Rudess in 1999.
To date, Dream Theater has released fourteen studio albums. Their first album, When Dream and Day Unite, was released in 1989 and is the only record to feature Dominici on vocals. The band's highest-selling release is their second album Images and Words (1992), which reached No. 61 on the Billboard 200 chart. Both the albums Awake (1994) and Six Degrees of Inner Turbulence (2002) also entered the charts at No. 32 and No. 46, respectively, and received critical acclaim. Their fifth album, Metropolis Pt. 2: Scenes from a Memory (1999), was ranked number 95 on the October 2006 issue of Guitar World magazine's list of The greatest 100 guitar albums of all time. It is ranked as the 15th Greatest Concept Album as of March 2003 by Classic Rock Magazine.As of 2018, Dream Theater has sold over 12 million records worldwide and has received two Grammy Award nominations. Along with Queensrÿche and Fates Warning, the band has been referred to as one of the "big three" of the progressive metal genre, responsible for its development and popularization.