His "pioneering fusion of ballet and modern dance challenged taboos and rattled purists but influenced major companies worldwide," wrote The New York Times in reporting the death.
Born in Cleveland in 1926 and raised near Pittsburgh, Tetley studied medicine and had a stint in the Navy before embarking on a career in dance. He trained in classical ballet with Helene Platova, Antony Tudor and Margaret Craske and at George Balanchine's School of American Ballet. He also studied modern dance with Hanya Holm and Martha Graham.
When Holm staged Cole Porter's Kiss Me Kate, Tetley was her assistant; he also performed a solo choreographed by Agnes de Mille in the Broadway musical Juno.
Tetley was one of the original members of the Joffrey Ballet when the troupe formed in 1956; over the next few years, he also performed with Martha Graham's company, American Ballet Theater, other contemporary dance groups and New York City Opera and other contemporary dance groups. In 1961, he was a dancer in Jerome Robbins's company Ballets: U.S.A.
In 1962, Tetley began to choreograph; his first program was performed at New York's Fashion Institute of Technology and included the premiere of Pierrot Lunaire. He went on to choreograph for ABT, Dance Theater of Harlem, the Houston Ballet and the National Ballet of Canada. His works, which number over 50, were also performed by such companies as the San Francisco Ballet, the Feld Ballet and the early Joffrey Ballet.
During the 1970s, Tetley was artistic director of (at different times) the Netherlands Dance Theatre and the Stuttgart Ballet. In 1986, he choreographed his first work for the National Ballet of Canada, Alice. Shortly after he was appointed artistic associate of the company and remained there until 1989.
According to the Times, Tetley's work irked both traditionalists and modernists, particularly in the U.S.; the latter criticized him for using pirouettes and arabesques in Pierrot Lunaire. After the early 1970s, he spent less time with the modern dance troupes he nurtured, like Ballet Rambert in London and Netherlands Dance Theater. As he became associated with major ballet companies like the Royal Ballet in Britain, the Australian Ballet, the Stuttgart Ballet and the Royal Danish Ballet, his work reportedly became more accepted.
The Times writes that Tetley was essentially "Europe's favorite American choreographer, more honored in the Old World than the New." The paper adds that the starting point for Tetley, who was interested in Eastern religions, was usually intellectual or inspirational.
He died of melanoma, according to the Times.