Gerald Joseph Mulligan, also known as Jeru, was an American jazz saxophonist, clarinetist, composer and arranger. Though primarily known as one of the leading jazz baritone saxophonists—playing the instrument with a light and airy tone in the era of cool jazz—Mulligan was also a significant arranger working with Claude Thornhill, Miles Davis, Stan Kenton, and others. His piano-less quartet of the early 1950s with trumpeter Chet Baker is still regarded as one of the best cool jazz ensembles. Mulligan was also a skilled pianist and played several other reed instruments. Several of his compositions including "Walkin' Shoes" and "Five Brothers", have become standards.

The baritone saxophone is a member of the saxophone family of instruments, larger than the tenor saxophone, but smaller than the bass. It is the lowest-pitched saxophone in common use — the bass, contrabass and subcontrabass saxophones are relatively uncommon. Like all saxophones, it is a single-reed instrument. It is commonly used in concert bands, chamber music, military bands, big bands, and jazz combos. It can also be found in other ensembles such as rock bands and marching bands. Modern baritone saxophones are pitched in E♭.