Earlier today, Jean ‘Toots’ Thielemans died in a Brussels hospital at age 94, after a fall at his nearby home a few weeks ago. He reportedly died in his sleep. According to his manager, Veerle Van de Poel, there were no complications: “He died of old age, his body was simply worn out.”

Mr. Thielemans, a world-famous master of the jazz harmonica, was also renowned as a whistler and for playing the guitar. His own composition of “Bluesette,” which he recorded in Stockholm in 1962, became his landmark tune for the rest of his life. There are over one hundred cover versions of “Bluesette,” both vocal and instrumental (the lyrics of “Bluesette” were penned by lyricist Norman Gimbel who also wrote “The Girl from Ipanema”)

“Bluesette” (1962), whistling and guitar improvisations by Jean ‘Toots’ Thielemans, who also composed the song

In his long and rewarding career as a jazz musician—he was by many considered to be one of the best in the genre—Mr. Thielemans worked with all the greats, from Édith Piaf, Benny Goodman, Peggy Lee, Duke Ellington, Charlie Parker, Miles Davis, Ella Fitzgerald, and Quincy Jones, to Frank Sinatra, Stevie Wonder, Johnny Mathis, Paul Simon, Billy Joel, and many more.

Billy Joel introducing Toots Thielemans to his audience as ‘the best harmonica player in the world,’ when performing his hit song “Leave a Tender Moment Alone” live on the London stage in the early 1980s

Mr. Thielemans was born in a working-class family in Brussels, April 1922, as Jean-Baptiste Frederic Isidore Thielemans. His parents ran a cafe on the same street where painter Pieter Bruegel the Elder lived in the 16th century. Thielemans first came to prominence in 1950 when Benny Goodman asked him to join him on his European concert tour. Later, Mr. Thielemans moved to New York, became a U.S. citizen in 1957, and since then commuted frequently between the U.S. and Belgium.

His harmonica was featured on several soundtracks over the years, most prominently when John Barry asked him to play the instrument on the theme song of “Midnight Cowboy” (1969), winner of three Academy Awards, including Best Picture. The film was directed by John Schlesinger and launched the careers of Dustin Hoffman, John Voight, and Brenda Vaccaro. Other harmonica solos of his can be heard in films such as “The Getaway” (1972), “Cinderella Liberty” (1973), Paul Verhoeven’s “Turkish Delight” (1973), “The Sugarland Express” (1974) for Steven Spielberg, “Arthur” (1981) starring Dudley Moore, and Claude Berri’s French screen classics “Jean de Florette” and “Manon de Source” (both 1986, starring Yves Montand).

The theme song from John Schlesinger’s “Midnight Cowboy” (1969); music by John Barry, harmonica solo by Jean ‘Toots’ Thielemans

Two years ago, Mr. Thielemans officially retired from live performing. Today, all international media are reporting his death. He was, after all, an unrivaled master of the harmonica and musical virtuoso; you’ll just know if you’d care to listen to the way he could revive a song like “What a Wonderful World”—there was no one else around who could play it on the harmonica as Mr. Thielemans did.

Mr. Thielemans, age 90, playing “What a Wonderful World” live in Liège, elgium, in 2012, vocals by Trijntje Oosterhuis