A master of the French horn, a rarity in jazz, he toured the world with the pianist Dwike Mitchell and taught music at Yale.Willie Ruff, who fashioned an unlikely career in jazz as a French horn player and toured the world as a musical missionary in the acclaimed Mitchell-Ruff Duo while maintaining a parallel career at the Yale School of Music, died on Sunday at his home in Killen, Ala. He was 92.His death was confirmed by his niece Jennifer Green.Mr. Ruff, who was also a bassist, played both bass and French horn in the duo he formed with the pianist Dwike Mitchell in 1955, which lasted until Mr. Mitchell’s death in 2013. They opened for many jazz luminaries, including Duke Ellington, Miles Davis and Sarah Vaughan; played countless concerts in schools and colleges; and toured foreign countries where jazz was little known or even taboo.In 1959, they flouted edicts against music that the Soviet Union deemed bourgeois, performing an impromptu set in Moscow while on tour with the Yale Russian Chorus. Their concerts in China in 1981 were considered the first jazz performances there since the Cultural Revolution.A globe-trotting musical career, however, seemed a remote possibility when Mr. Ruff was growing up in a small Southern town during the Great Depression.Mr. Ruff, left, and Dwike Mitchell, right, in November 1959 with the classical pianists Lev Vlassenko, second from left, and Van Cliburn. Mr. Ruff and Mr. Mitchell met in the Army and in 1955 formed the Mitchell-Ruff Duo, which stayed together until Mr. Mitchell’s death in 2013.Associated PressHe was born on Sept. 1, 1931, in Sheffield, Ala., the sixth of eight children of Willie and Manie Ruff. “We lived in a house — my mother and eight children — that had no electricity, so there was no radio or music,” he said in a 2017 interview with Yale. “But there was always dancing, to silence. The dances made their own rhythm.”He eventually learned to pound out his own rhythms on piano and drums. At 14, he fudged his way into the Army, on the advice of an older cousin who had enlisted at 17 with his parents’ permission and dismissed Mr. Ruff’s concern that he was too young: “For a musician, you sure are dumb,” Mr. Ruff recalled the cousin saying. “Don’t you know how to write your daddy’s name?”He hoped to leverage his skill with the sticks into a spot in a highly regarded all-Black military band, but, seeing a glut of drummers, he took up the French horn instead. It was in that band that he met Mr. Mitchell, who taught him to play the stand-up bass.After leaving the Army, Mr. Ruff applied to the Yale School of Music, hoping to use his financial windfall from the G.I. Bill of Rights to study with the famed composer Paul Hindemith. “I brought my French horn and played an audition, and by some miracle they let me in,” he said in an interview with the quarterly newspaper The Soul of the American Actor. “So, Uncle Sam put me through my schooling!”He earned his bachelor’s degree in 1953 and his master’s degree a year later. In 1955, he was weighing an opportunity to join the Israel Philharmonic Orchestra when he turned on “The Ed Sullivan Show” and saw his old friend Mr. Mitchell at the piano, as a member of Lionel Hampton’s band. He called him at the television studio, and Mr. Mitchell soon recruited Mr. Ruff to play in the band.Playing an instrument associated with classical music in a jazz band was unconventional, but it opened doors for Mr. Ruff, as did the broad musical training he had received at Yale.“Lionel Hampton’s band was the worst-paying, hardest-working band in the world,” he recalled in an interview for Yale’s Oral History of American Music project. “So if a saxophone player quit, I played his part. If a trombone player quit, I played his part, and that would make me valuable because I could transpose all these parts.” With no parts written for the French horn itself, he said, Mr. Hampton “didn’t know what to expect”:“As long as it worked, I was left to invent. It was wonderful training.”From left, Charles Mingus, Duke Ellington and Mr. Ruff in 1972, the year Mr. Ruff founded the Ellington Fellowship program at Yale.Reggie Jackson/Yale University Art GalleryMr. Ruff joined the Yale faculty in 1971 and stayed until he retired in 2017. In 1972 he founded the Ellington Fellowship, which is dedicated to expanding the study of African American music and has honored a long list of jazz notables, some of whom performed concerts in New Haven, Conn., and shared their musical knowledge with hundreds of thousands of local public school students.His immediate survivors include a brother, Nathaniel. His wife, Emma, and daughter, Michelle, died before him.Late in his life, Mr. Ruff recalled that his turn to education seemed almost predestined. When he was in second grade, W.C. Handy, the composer and musician known as “the father of the blues,” who was from nearby Florence, Ala., visited his class. He played trumpet for the students and talked to them about “how important it was to continue our education and hold up our heritage and our culture,” Mr. Ruff told Yale in 2017. “He said that it’s not from royalty or from the highborn that music comes, but it is often from those who are the farthest down in society.”“After he finished,” Mr. Ruff added, “all the children who were musically inclined were permitted to shake the hand of the man who wrote ‘The Saint Louis Blues.’”“I was never the same boy again,” he recalled. “I had to be a teacher.” More