September 18, 2014 6:33 AM EDT

Whenever young Bill Cosby visited his grandparents as a child, his Granddad Samuel would tell him stories from the Bible. But rather than just offer recitations, Samuel turned his tales into full-on performances, creating narratives filled with uniquely voiced characters and ending with strong moral lessons. Those encounters, according to Mark Whitaker’s new biography, Cosby, shaped the premier comic storyteller of our time. But Whitaker goes beyond the jokes, illuminating Cosby’s personal life–with one glaring omission–from an impoverished Philadelphia upbringing with a mercurial father to his comedic rise in Greenwich Village bars to his career as a television pioneer who revolutionized not just comedy but the nation’s perception of black America.

Born in 1937, Cosby was already noted in the fifth grade as a deft, amusing storyteller with a talent for lifting spirits. As a physical-therapy technician in the Navy, he regaled hospital patients with tales that had them laughing so uproariously, the lieutenant in charge feared stroke patients would relapse. As a fledgling comic influenced by bebop jazz and Mel Brooks and Carl Reiner’s “2,000 Year Old Man” routine, he exploited his gift for improvisation at New York City’s Gaslight Café–where he often slept in the same tiny storeroom in which Bob Dylan wrote the lyrics to “A Hard Rain’s A-Gonna Fall”–bringing loose outlines to the stage, then riffing in ways that rendered every performance unique.

Booked on Johnny Carson’s Tonight Show, Cosby delivered a set that so enchanted 16-year-old Rob Reiner that he told his father Carl, who introduced Cosby to the producer of I Spy. When Cosby landed a lead role in the 1965 series, Variety proclaimed him “television’s Jackie Robinson.” Success reinforced Cosby’s confidence in dealing with the turbulent racial issues of the 1960s. He viewed racism as an obstacle best conquered not through battle but achievement. Many in the black community perceived his lack of outspokenness as a desire to suck up to white people, but Cosby thought the best way he could support African Americans was by hiring them. He did that in abundance, giving early breaks to the likes of Melvin Van Peebles and Samuel L. Jackson. He also advocated for education, giving generously to historically black colleges, including $20 million to Spelman College.

Launched in 1984, The Cosby Show was so closely based on his own family that Cosby sometimes slipped and referred to Cliff Huxtable as Bill. The show was credited not only with reviving NBC but also with the “Cosby effect,” in which images of black success helped Americans eventually feel comfortable electing our first black President.

Cosby covers many tough episodes, including the comedian’s estrangement from wild-child daughter Erinn and the 1997 murder of his son Ennis, but the book falters in a glossed-over take on Cosby’s “roving eye.” Whitaker mentions infidelities so casually that it leaves the reader, who has otherwise heard only of Cosby’s devotion to wife Camille, with whiplash. Worse, the book omits accusations that Cosby drugged and sexually assaulted as many as 13 women from the 1970s to 2004. (While Cosby has denied the allegations through his attorneys and no criminal charges were ever filed, he did settle one civil case in which a woman claimed he had drugged and raped her.)

Whitaker notes that after first declining, Cosby gave him 15 hours of interviews and opened doors to sources. Did that cooperation come with conditions? Cosby’s incomplete portrait leaves the reader feeling that at least one aspect of the man remains, and will continue to be, a paradox.

This appears in the September 29, 2014 issue of TIME.

More Must-Reads From TIME

Contact us at letters@time.com.

You May Also Like