The Crusades of Cesar Chavez. By Miriam Pawel. Bloomsbury; 588 pages; $35. To be published in Britain in May; £25. Buy from,

ON THE last day of March, California, Colorado and Texas celebrated Cesar Chavez day, marking the memory of a man who is the closest thing America’s 53m Latinos have to a Martin Luther King. The date is Chavez’s birthday; it was also, he would tell journalists, the anniversary of the day in 1962 when he resigned from a community service group to form his farmworkers’ union. Yet among the revelations of Miriam Pawel’s detailed biography, which will become the definitive life, is the news that he actually quit two weeks earlier. A minor infraction, perhaps, but it illuminates how willing the man, whom many came to see as saintlike, was to construct his own creation myths.

Ms Pawel, a former journalist, regards earlier Chavez lives as hagiography. She might say the same of a new Hollywood film directed by Diego Luna. Her book, by contrast, does not shy from the more troubling sides of her subject. Charismatic, if unprepossessing in his plaid shirt and olive trousers, the gap-toothed Chavez inspired thousands of Hispanic and Filipino farmworkers to down tools on grape farms in California’s Central Valley with cries of “Huelga!” (strike). Crippling consumer boycotts, organised by Chavez-followers across America, drove intransigent growers to negotiation and sometimes capitulation. Farmers who had sworn they would never recognise farmworkers’ collective representation found themselves signing away their hiring rights.

Chavez was a media-savvy pragmatist not averse to dealmaking. Yet unlike the hard-headed Anglos who ran the industrial unions, he saw himself more as a spiritual guide than a labour leader. He despaired of the tendency among poor workers he helped to desire colour televisions and golf clubs as they grew richer. He distrusted colleagues who sought pay rises, and rejected them for himself; sacrifice, he urged, must be the mark of the movement. He embarked on regular fasts, both to draw attention to the cause and, in trying times, to strengthen his own fortitude. Gandhi, rather than King, was the role model.

Such personal commitment inspired fathomless devotion among Chavez’s acolytes, among them student dropouts, wealthy socialites and Bobby Kennedy, as well as members of Chavez’s United Farm Workers Union (UFW). Legal reforms were achieved, rival unions stared down. But Chavez’s single-mindedness also brought forth eccentric decision-making, autocratic leadership and administrative chaos that would ultimately undo a lot of the earlier good work. Many cesarchavistas, for example, were dismayed by their hero’s dalliance in the late 1970s with the leader of a drug-rehabilitation group with cultlike qualities, who advocated mandatory vasectomies for men.

By the time of Chavez’s death in 1993 the UFW had dwindled to around 20,000 members from a peak of 80,000 in the early 1970s. He was lauded more by politicians in distant states seeking the glow of his aura than by those who knew him. The endless schools named after him were populated with children who knew more about his namesake, a world-champion boxer, than the man who had inspired their parents to form picket lines.

Today Chavez’s memory is being pressed into service in the fight to reform America’s immigration system, including legalisation for the 11m-12m illegal migrants. There is an irony here; Chavez was hostile to illegal Mexican workers for undercutting his ability to withdraw labour from the fields, even reporting some to officials. Yet were he alive today he would surely not be deaf to the laments of the families broken by America’s deportation machine. His battle cry ¡Sí Se Puede! (later adapted by candidate Barack Obama) was originally formulated as a response to cynics who said change was impossible.