In the early stages of their career, Dream Theater were known as Majesty (named after Mike’s description of the song “Bastille Day” by Rush). However, before the recording of When Dream and Day Unite another band named Majesty got in contact with DT ordering them to change their name.
Various names were considered (“Glasser” was the band’s official name for about a week), but the honour of being the person that suggested “Dream Theater” goes to Mike Portnoy’s father, Howard Portnoy. He suggested the name based on the (now-demolished) theater in Monterrey, California. The name stuck. Mike got a message on his answering machine from his father telling him about a movie theater in California called the Dream theater, and the band liked it so much they used it for their band name.
In 2002 the theater was demolished, much to the dismay of local DT fans.