Jean-Baptiste Frédéric Isidor, Baron Thielemans (29 April 1922 – 22 August 2016), known professionally as Toots Thielemans, was a Belgian jazz musician. He was mostly known for his chromatic harmonica playing, as well as his guitar and whistling skills, and composing.

According to jazz historian Ted Gioia, his most important contribution was in "championing the humble harmonica", which Thielemans made into a "legitimate voice in jazz". He eventually became the "preeminent" jazz harmonica player. His first professional performances were with Benny Goodman's band when they toured Europe in 1949 and 1950.