He could also be called a white man's worst fear. I enjoyed this snippet from a review of Grant's book in The New Yorker,
In 1914, on a ship between Jamaica and England, an impoverished twenty-six-year-old named Marcus Garvey had what he later called a vision of "a new world of black men." Six years later, he rode through Harlem in regal robes and a plumed bicorne, and was proclaimed the Provisional President of Africa before a crowd of twenty-five thousand in Madison Square Garden. For a short, spectacular time, before his movement collapsed under the weight of its ambitions and schemes (a mail-fraud conviction resulted in exile in London), Garvey’s call for a transnational union of black people electrified crowds around the world—alarming J. Edgar Hoover and maddening W. E. B. Du Bois, who recoiled at Garvey’s separatism and his theatrics, wondering if he was "a lunatic or a traitor." (Garvey called Du Bois a "lazy dependant mulatto.") Grant’s biography ably captures the Garvey moment, although, perhaps wisely, he leaves the many contradictions in Garvey’s character unresolved.
Garvey has taken on mythic proportions over the years, as much reviled as idolized for his flamboyant and fascist inclinations. Grant's book does look interesting.