John Francis Anthony “Jaco” Pastorius III (/ˈdʒɑːkoʊ pæˈstɔːriəs/; December 1, 1951 – September 21, 1987) was an American jazz bassist who was a member of Weather Report from 1976 to 1981. He worked with Pat Metheny and Joni Mitchell, and recorded albums as a solo artist and band leader. His bass playing employed funk, lyrical solos, bass chords, and innovative harmonics. As of 2017, he is the only electric bassist of seven bassists inducted into the DownBeat Jazz Hall of Fame, and has been lauded as one of the best electric bassists of all time.

Pastorius suffered from drug addiction and mental health problems throughout his professional life, and despite his widespread acclaim, over the latter part of his life he had problems holding down jobs due to his unreliability. In frequent financial trouble, he was often homeless throughout the mid 1980s. He died in 1987, as a result of injuries sustained in a fight outside of a South Florida music club.

After his death, his work continued to influence musicians. He was elected to the DownBeat Hall of Fame in 1988. He was the subject of the 2014 documentary film Jaco.

John Francis Pastorius was born December 1, 1951, in Norristown, Pennsylvania. He was the oldest of three boys born to Stephanie, his Finnishmother, and Jack Pastorius, a singer and jazz drummer who spent much of his time on the road. His family moved to Oakland Park near Fort Lauderdale when he was eight.

Pastorius’ nickname, “Jaco”, became adopted, and was partially influenced by his love for sports as well as the umpire Jocko Conlan. In 1974, he began spelling it “Jaco” after it was misspelled by his neighbor, pianist Alex Darqui. His brother called him “Mowgli” after the wild boy in The Jungle Book because he was energetic and spent much of his time shirtless on the beach, climbing trees, running through the woods, and swimming in the ocean. He attended St. Clement’s Catholic School in Wilton Manors and was an altar boy at St. Clement’s Church. His confirmation name was Anthony, thus expanding his name to John Francis Anthony Pastorius. He was intensely competitive and excelled at baseball, basketball, and football.

He played drums until he injured his wrist playing football when he was thirteen. The damage was severe enough to warrant corrective surgery and inhibited his ability to play the drums. By 1968–1969, at the age of 17, Pastorius had begun to appreciate jazz and had saved enough money to buy an upright bass. Its deep, mellow tone appealed to him, though it strained his finances. He had difficulty maintaining the instrument, which he attributed to the humidity in Florida. When he woke one day to find it had cracked, he traded it for a 1962 Fender Jazz Bass. In his teens he played bass guitar for Wayne Cochran and the C.C. Riders. In the early 1970s, Pastorius taught bass at the University of Miami, where he befriended jazz guitarist Pat Metheny, who was also on the faculty. With Paul Bley, Pastorius and Metheny recorded an album, later titled Jaco (Improvising Artists, 1974). Pastorius then played on Metheny’s debut album, Bright Size Life(ECM, 1976). He recorded his debut solo album, Jaco Pastorius (Epic, 1976) with Michael Brecker, Randy Brecker, Herbie Hancock, Hubert Laws, Pat Metheny, Sam & Dave, David Sanborn, and Wayne Shorter.