Otis Spann (March 21, 1930 – April 24, 1970) was an American blues musician whom many consider to be the leading postwar Chicago blues pianist. Born in Jackson, Mississippi, United States, Spann became known for his distinct piano style.

Spann's father was reportedly a pianist called Friday Ford. His mother Josephine Erby was a guitarist who had worked with Memphis Minnie and Bessie Smith, and his stepfather Frank Houston Spann was a preacher and musician. One of five children, Spann began playing piano at the age of seven, with some instruction from Friday Ford, Frank Spann, and Little Brother Montgomery. At the age of 14, he was playing in bands around Jackson, finding more inspiration in the 78s of Big Maceo Merriweather. It was Merriweather who took the young pianist under his wing once Spann migrated to Chicago in 1946. Spann gigged on his own, and with guitarist Morris Pejoe, working a regular spot at the Tic Toc Lounge.
Spann replaced Merriweather as Muddy Waters' piano player in late 1952, and participated in his first recording session with the band on September 24, 1953. From 1952 to 1968 Spann was a full-time member of the Muddy Waters band, while periodically recording as a solo artist. In that period he also did session work with other Chess artists like Howlin' Wolf and Bo Diddley.

Spann's own Chess Records output was limited to a 1954 single, "It Must Have Been the Devil" / "Five Spot", which featured B.B. King and Jody Williams on guitars, and two sides recorded in 1956 with a band featuring Big Walter Horton and Robert Lockwood that were unreleased at the time. He recorded a session with the guitarist Robert Lockwood, Jr. and vocalist St. Louis Jimmy in New York on August 23, 1960, which was issued on Otis Spann Is The Blues and Walking The Blues. A largely solo outing for Storyville Records in 1963 was recorded in Copenhagen. A set for UK Decca Records the following year found him in the company of Muddy Waters and Eric Clapton, and a 1964 album for Prestige followed where Spann shared vocal duties with band-mate James Cotton.
The Blues is Where It's At, Spann's 1966 album for ABC-Bluesway, sounded like a live recording. It was a recording studio date, enlivened by enthusiastic onlookers that applauded every song (Muddy Waters, guitarist Sammy Lawhorn, and George "Harmonica" Smith were among the support crew). A Bluesway encore, The Bottom of the Blues followed in 1967 and featured Spann's wife, Lucille Jenkins Spann (June 23, 1938 – August 2, 1994), helping out on vocals.
In the late 1960s, he appeared on albums with Buddy Guy, Big Mama Thornton, Peter Green and Fleetwood Mac.

Following his death from liver cancer in Chicago in 1970, at the age of 40, he was interred in the Burr Oak Cemetery, Alsip, Illinois. Spann's grave laid unmarked for almost thirty years, until Steve Salter (president of the Killer Blues Headstone Project) wrote a letter to Blues Revue magazine to say "This piano great is lying in an unmarked grave. Let's do something about this deplorable situation". Blues enthusiasts from around the world sent donations to purchase Spann a headstone. On June 6, 1999 the marker was unveiled during a private ceremony. The stone reads "Otis played the deepest blues we ever heard - He'll play forever in our hearts".
He was posthumously elected to the Blues Hall of Fame in 1980.