Michael Stephen "Mike" Portnoy is an American drummer primarily known as the former drummer, backing vocalist, and a co-founder of the progressive metal band Dream Theater. Known for his drumming prowess and technical skill, Portnoy has won 23 awards from the Modern Drummer magazine. He has co-produced the last six Dream Theater albums with guitarist John Petrucci, starting from Metropolis Pt. 2: Scenes from a Memory. From A Change of Seasons onwards, Portnoy had been writing a substantial amount of Dream Theater's lyrics. He is the second youngest person (after Neil Peart) to be inducted into the Modern Drummer's Hall of Fame (at 37 years of age).

On September 8, 2010, it was announced that Portnoy had left Dream Theater. Portnoy cited conflicting interests as the reason behind his departure.

On February 3, 2011, Portnoy announced that he has started a new project with Symphony X singer Russell Allen and guitarist Mike Orlando. Also he is involved in various projects with Neal Morse.