That’s not to speak of the damage he did to his work: the last-minute cancellations, the no-shows. In a famous story, he walked onstage at the Aladdin in Las Vegas, went to the mike, said, “What the fuck am I doing here?” and walked off. In another incident, in a show advertised as being in support of “human rights” (by which the producers meant gay rights, but they wouldn’t say so), he invited the audience to kiss his black ass and told them about how, when he was young, he had enjoyed sucking somebody or other’s dick. This was at the Hollywood Bowl, with an audience of seventeen thousand. If people were offended by his remarks, he said, “I hope y’all get raped by black folks with clap.” Elsewhere, he boasted publicly of how much cocaine he had consumed: “I could have bought Peru for all the shit I snorted.”

It’s amazing, given this record, how many producers rehired him, and just took out more insurance. Not all of them, though. Notoriously, Pryor lost the role of Sheriff Bart, in “Blazing Saddles,” to Cleavon Little because, reportedly, the producers believed that Little was less likely than Pryor to destroy himself on drugs in the course of the shooting. Mel Brooks told Saul that he went down on his knees to the Warner Brothers bosses to get them to change their minds. They refused.

In 1980 came the famous self-immolation incident. Saul, braiding several strands of evidence (including Pryor’s own account), claims that what happened was not an accident, as is so often said, but a sort of perverse improvisation. Pryor’s beloved grandmother Marie died at the end of 1978, which, according to Saul, plunged him into a long, harrowing depression. One night, in June of 1980, he was at home, in Los Angeles. Courtesy of his freebase pipe, he had not slept in five days. He was watching a television program that included footage of a Buddhist monk, in Vietnam, setting himself on fire. As Pryor later recalled, he was trying, at that moment, to talk to God. “What do you want me to do?” he asked his maker. Receiving no answer, he poured a bottle of liquor over his head, soaking himself down through his shirt, and then set himself on fire with a cigarette lighter. His bodyguard and his aunt, who were present, tried to quench the flames, but he decided that they were aiming to smother him. He ran out of the house, down its long, curving driveway, and onto the sidewalk, still expostulating with the Almighty: “Lord, give me another chance…. Haven’t I brought happiness to anyone in this world?”

By this time, apparently, the fire was extinguished, and his polyester shirt had melted onto his chest. As he remembered it, he smelled like “a burned piece of meat.” The police had been called, and an officer was now trotting along behind Pryor, asking him please to stop. He wouldn’t. Finally, when he had got about a mile from his house, the fire-department medics arrived. They grabbed him, put him in an ambulance, and took him to the burn unit of Sherman Oaks Community Hospital.

As you read of this event, you may notice, to your surprise, that you are very few pages (thirteen) from the end of the book. Pryor was only thirty-nine years old when he set himself on fire, and his biggest commercial successes were still ahead of him. Does Saul really mean to conclude his narrative now? Yes. His book, he writes, “is about the shaping of a talent until it rose to the level of its full genius.” For that reason, he says, the story ends with the film “Richard Pryor: Live in Concert” (1979). Among the events surrounding that project were Marie’s death, the terrible depression, and then the fire. In the process, Saul claims, Pryor cast away “a crucial part of his artistic self: the love of experiment.”

Once he emerged from treatment, Pryor was a changed man, much tamer. In a way, he had gotten his wish: he was Cosby! (One barely needs to point out the ironies here. To many people today, Cosby looks like the reprobate, and Pryor the honest citizen.) Of the movie “Brewster’s Millions,” from 1985, the Times critic Vincent Canby, who had adored Pryor, said that he felt as though he were looking at “the extremely busy shadow of someone who has disappeared.” Pryor acknowledged that he was now a different person, and he seemed to know that something had been lost. But, as he told a journalist, “at least … I’m not waking up saying, ‘Oh, no, did I kill someone last night?’ ” If the fire slowed him down artistically, a larger impediment arose soon afterwards. In 1986, Pryor was diagnosed with multiple sclerosis, and from then on he worked less and less, though it was not until 2005, when he was sixty-five, that he died, of a heart attack. Basically, he had one decade of greatness, the seventies.

One can sympathize with Pryor’s relief at waking up in the morning without having to wonder if the police were coming, but one can also understand Saul’s reluctance to take us through the artistic consequences of Pryor’s new respectability. Consider just one thing: Pryor’s constant use, in the sixties and seventies, of the word “nigger.” Already, at the time, this was awkward for critics. Today, when we are more subject than ever to political language codes, it is a greater focus of dispute—for users and for disapprovers, black and white. Saul points out that Pryor started saying “nigger” when he began making comedy out of character sketches, inspired by the world he had been born into. “You cannot represent that world without using that word,” Saul says. Other commentators have offered more complicated explanations. But one should be careful not to rationalize the term, detoxify it, pat it on the head and say, Don’t worry, we know you didn’t mean to be bad. No, Pryor used it partly because he liked to be bad, and to drive moralists nuts. Saul is true to that fact throughout the book, and so, in walking away from the post-immolation material, he is not being unfaithful to Pryor.

In the process, he does lose a few important things—for example, the 1982 concert album “Richard Pryor: Live at the Sunset Strip,” so full of wonderful material: the poetic monologue for Mudbone, Pryor’s garrulous old know-it-all character; the story of Pryor’s trip to Africa, with its superb animal imitations; the playlet about Italian mobsters, which I think is the funniest routine ever created about any ethnic group. What do these items have in common apart from their great artistry? Most of them back off from Pryor’s usual overt concern with racism. Actually, they don’t just back off; they declare that they’re doing so. Pryor tells us that when he was in Africa he decided that he wasn’t going to say “nigger” any more. He looked out his hotel window, he said, and saw all these lovely black people and concluded that the word was demeaning. In “Sunset Strip” he also explains the self-immolation episode in a way that is, for him, notably self-accusatory. In other words, Pryor, in this album, is moving as far away from his bad-boy persona as he can without abandoning comedy. However artistic the resulting material, it may still have looked to Saul like self-betrayal. Pryor was clearly an exhausting subject, one who was constantly pushing Saul into the position of moralist or mental-health counsellor, rather than what he clearly wanted to be: an arts critic.