A detailed and well-rounded biography of Ailey (1931-89), the celebrated African-American dancer and choreographer. New York Times dance critic Dunning (""But First a School,"" 1985) here considers a subject whose volatility and well-known penchant for privacy to some extent obstruct her desire to explain him. Born in a rural cabin near Rogers, Tex., Ailey was abandoned by his father when he was three months old. As a boy, he followed his mother from job to job until they ended up in Los Angeles in 1942. Alley the teenager was magnetized by poetry, music, theater, movies, and dance--especially by the wrought Caribbean extravaganzas of Katherine Dunham. Alley studied dance locally with Lester Horton, eventually joined and choreographed for his company, then left for the East to appear in the show House of Flowers. His tumultuously productive professional life ultimately saw the triumph of his vision of African-American identity in such dances as Cry and Revelations and the achievement of interracial artistic harmony in his integrated company, the Alvin Alley American Dance Theater. Though the book is held back at times by the spirit of boosterism (e.g., ""The kid from Texas had climbed to another summit""), usually Dunning takes care not to romanticize the endless strains and difficulties involved with sustaining choreographic creation and long-term institutional stability. Nor does she neglect the paradoxes of Alley, a manic-depressive and often self-destructive man whose drug habit and promiscuous erotic love for men raised eyebrows and occasionally led to skirmishes with police. The best part of the book may be its last quarter, when Dunning is compelled to confront the dancer's secrecies head-on, and when she movingly narrates his decline and death from AIDS. One is left with the impression that perhaps no one understood Alley, not even Ailey himself. But there is plenty of reason to wish we did, and Dunning provides a very useful point of entry.