Michael Peter Balzary (born October 16, 1962), known professionally as Flea, is an Australian and American musician and actor. He is a founding member and bassist of the rock band Red Hot Chili Peppers. Flea and vocalist Anthony Kiedis are the only two continuous members of the band and the only ones to appear on every album. Flea is also a member of the supergroups Atoms for Peace, Antemasque, Pigface, and Rocket Juice & the Moon, and has played with acts including the Circle Jerks, the Mars Volta, Johnny Cash, Tom Waits, Alanis Morissette, Young MC, Nirvana, What Is This?, Fear, and Jane's Addiction.

Flea's playing incorporated elements of funk (including prominent slap bass), psychedelia, punk, and hard rock. In 2009, Rolling Stone readers ranked Flea the second-best bassist of all time, behind John Entwistle. In 2012, he and the other members of Red Hot Chili Peppers were inducted into the Rock and Roll Hall of Fame.

Flea has acted in films and television series such as Suburbia, Back to the Future Part II and Part III, My Own Private Idaho, The Chase, Fear and Loathing in Las Vegas, Dudes, Son in Law, The Big Lebowski, Low Down, Baby Driver, Boy Erased, The Wild Thornberrys, Obi-Wan Kenobi, and Babylon. He is the co-founder of Silverlake Conservatory of Music, a non-profit organization founded in 2001 for underprivileged children. In 2019, he published a memoir of his early life, Acid for the Children.

Michael Peter Balzary was born on October 16, 1962, in Melbourne, Victoria, Australia. He is of partial Hungarian and Irish descent. His father, Mick Balzary, an avid fisherman, often took him fishing. When Flea was four, his family moved to Rye, New York, US for his father's career. In 1971, his parents divorced, and his father returned to Australia. Flea and his sister Karyn stayed with their mother Patricia, who subsequently married jazz musician Walter Urban (1941–2011).

Flea's stepfather frequently invited musicians to his house for jam sessions. The family moved to Los Angeles, California, where Flea became fascinated by the trumpet. He attended private lessons taught by Jane Sager. He had no interest in rock music at the time, instead idolizing jazz musicians like Miles Davis, Louis Armstrong, and Dizzy Gillespie. Flea described his childhood home as violent; his stepfather was an aggressive alcoholic who eventually became involved in shootouts with police. Flea said: "I grew up being terrified of my parents, particularly my father figures. It caused [me] a lot of trouble later in life." To cope, Flea began smoking cannabis at 13, and became a daily user.

He was first called "Flea" as a teenager for his seeming inability to sit still, and the nickname stuck. Nicknamed Mike B. the Flea, he attended Fairfax High School, and was something of an outcast due to his taste in music. However, he soon met Anthony Kiedis, and after a brief confrontation (which involved Kiedis putting a loaded .44 Magnum to Balzary's head), the two became best friends. Kiedis recalled: "We were drawn to each other by the forces of mischief and love and we became virtually inseparable. We were both social outcasts. We found each other and it turned out to be the longest-lasting friendship of my life."

Flea was introduced to rock music by Hillel Slovak, and particularly punk rock by Kiedis. Flea learned to play bass from Slovak, who shortly after asked him to be a bassist in his band, Anthym. Flea soon developed his own style and joined the group, but quit several months later to play for the punk rock outfit Fear. He then rejoined Slovak to form an intended one-off band: Tony Flow and the Miraculously Majestic Masters of Mayhem along with Kiedis and Jack Irons, all of them at the time inspired by the free funk band Defunkt and the hip-hop act Grandmaster Flash and the Furious Five.

The band changed its name to the Red Hot Chili Peppers, playing several shows at L.A. venues. Their repertoire grew to nine songs as a result of months of playing at local nightclubs and bars. The Red Hot Chili Peppers entered Bijou Studios to record a demo tape produced by the then-drummer of Fear and subsequently secured a record deal with EMI. Irons and Slovak, however, decided to leave the Red Hot Chili Peppers in order to pursue a "more serious" future with the rock band What Is This?. Flea ultimately respected the decision, but felt the band would be lost without them. He and Kiedis hired drummer Cliff Martinez and guitarist Jack Sherman to fill Irons' and Slovak's place, respectively. Andy Gill, formerly of Gang of Four, agreed to produce their first album. Gill and Sherman clashed with Flea and Kiedis; they continuously argued over music style, sound, and the album's production. Flea himself felt that the album was stiff and "a big mistake", but also admitted, "we [he and Kiedis] were just disrespectful and obnoxious". The band's debut album, The Red Hot Chili Peppers, was released on August 10, 1984, to largely poor critical and commercial review. After a relatively unfruitful tour, Sherman was fired in early 1985. Slovak, who had been contemplating a return to the Chili Peppers, rejoined the group after being encouraged by Flea.