James M. (Jimmy) Knepper (born November 22, 1927 in Los Angeles, died 2003) was an American jazz trombonist.

He was associated with the bassist and composer Charles Mingus but allegedly did not get along with him. Knepper was twice on the receiving end of Mingus' legendary temper. While onstage at a memorial concert in Philadelphia, he reportedly attempted to crush his pianist's hands with the instrument's keyboard cover, then punched Knepper in the mouth. On October 12, 1962, Mingus reportedly punched Knepper while the two men were working together at Mingus's apartment on a score for his upcoming concert at New York Town Hall and Knepper refused to take on more work. The blow broke one of Knepper's teeth, ruined his embouchure and resulted in the permanent loss of the top octave of his range on the trombone. This attack ended their working relationship and Knepper was unable to perform at the concert, a disaster. Charged with assault, Mingus appeared in court in January, 1963 and was given a suspended sentence.

Discography

• A Swinging Introduction to Jimmy Knepper - Bethlehem (1957)
• Idol of the Flies - Bethlehem (1957)
• Pepper-Knepper Quintet - MGM (1958)
• Pepper and Knepper - Metrojazz (1958)
• Cunningbird - Steeple Chase (1976)
• Jimmy Knepper in L.A. - Inner City (1977)
• Tell Me... - Daybreak (1979)
• Primrose Path - HEP (1980)
• First Place - Black Hawk (1982)
• I Dream Too Much - Soul Note (1984)
• Dream Dancing - Criss Cross (1986)