Michael Stephen Portnoy[2] (born April 20, 1967) is an American musician who is primarily known as the drummer, backing vocalist, and co-founder of progressive metal band Dream Theater.

In September 2010, Portnoy announced his departure from Dream Theater after 25 years, with Mike Mangini taking his place as drummer of the band.

During his time out of Dream Theater, Portnoy remained active, with a variety of bands and projects, including Adrenaline Mob, Avenged Sevenfold, Transatlantic, Yellow Matter Custard, Flying Colors, The Winery Dogs, Liquid Tension Experiment, Metal Allegiance, Sons of Apollo, the Neal Morse Band, and BPMD.

Mike and his father later moved to Carmel-by-the-Sea, California, to work at KRML radio station after watching the 1971 film Play Misty for Me.

Portnoy left Inner Sanctum, his last high school band, after being awarded a scholarship to attend the Berklee College of Music in Boston.

In the spring of 2010, Portnoy filled in for Avenged Sevenfold's former drummer, Jimmy "The Rev" Sullivan, who died during the production of the band's fifth album Nightmare.

On May 5, 2010, Portnoy released a statement on his status with Avenged Sevenfold on their official website, concluding his working relationship with the band.

[9] Avenged Sevenfold chose not to continue working with Portnoy after the Nightmare tour was completed, in part due to the significant controversy surrounding his departure from Dream Theater.

He is also a founding member of Transatlantic, a progressive rock "super-group" featuring former Spock's Beard keyboardist/vocalist Neal Morse, Flower Kings guitarist Roine Stolt and Marillion bassist Pete Trewavas.

Portnoy has also recorded and/or toured/performed live with Umphrey's McGee, OSI, Hail!, Stone Sour, Fates Warning, Overkill and G3.

[21] In the April 2001 edition of Modern Drummer and Portnoy's website, he names Neil Peart, Ringo Starr, Phil Collins, John Bonham and Keith Moon as influences.

Before live performances of "Trial of Tears", he would sometimes switch instruments with John Petrucci and play a fragment of "Eruption" by Van Halen.

With all of the festivals and package tours that go through America, I've been talking with our manager and agent for over 10 years now about doing something that focuses on the more progressive, musician-oriented side of hard rock and metal.

Also rounding out the cruise were a large number of other progressive rock artists, Jon Anderson, Adrian Belew's Power Trio, Devin Townsend Project, King's X, Spock's Beard, The Flower Kings, Pain of Salvation, Anathema, Riverside, Periphery, Animals as Leaders, The Safety Fire, Tony Harnell & Bumblefoot, Beardfish, The Dear Hunter, Haken, Jolly, Anneke Van Giersbergen, Mark Mikel, and his son, Max Portnoy's band, Next to None.