John Francis Anthony Pastorius III (December 1, 1951 – September 21, 1987), known as Jaco Pastorius, was an American jazz musician and composer and electric bass player.

His playing style was noteworthy for containing intricate solos in the higher register and for the "singing" quality he achieved on the fretless bass. His innovations also included the use of harmonics. Pastorius suffered from mental illness including a substance-related disorder, and was diagnosed with bipolar disorder in 1982. He died in 1987 at age 35 following a violent altercation at a Fort Lauderdale bar.

Pastorius was inducted into the Down Beat Jazz Hall of Fame in 1988, one of only four bassists to be so honored (and the only electric bass guitarist). He is one of the most influential electric bass players of all time.