In 1972, a year after the release of his first album, “Just As I Am,” Bill Withers performed a song on British television. “Harlem,” the record’s first single, had done little on the charts, but radio d.j.s had picked up on its B-side. Wearing a ribbed orange turtleneck and sweating visibly, the thirty-three-year-old rookie introduced the first song he had ever written:

“Men have problems admitting to losing things,” he said. “I think women are much better at that. . . . So, once in my life, I wanted to forgo my own male ego and admit to losing something, so I came up with—” Withers began to play his acoustic guitar and sing. “Ain’t no sunshine when she’s gone / It’s not warm when she’s away / Ain’t no sunshine when she’s gone / And she’s always gone too long, any time she goes away.”

“Ain’t No Sunshine” gave Withers his first gold record, earned him a Grammy, and, with later hits such as “Lean on Me” and “Use Me,” forms the cornerstone of a small but indispensable section of the American songbook. A new documentary about Withers, “Still Bill,” is an unshowy, confident attempt to render the personality of a man who wrote so well and then walked away, in 1985, adding only a handful of songs to his legacy since then.

The sixth of six children, William Harrison Withers, Jr., was born on July 4, 1938, in Slab Fork, West Virginia. The town’s only viable industry was coal mining, and Bill, Jr., was the only man in his family who did not end up working in the mines. When he was three years old, his parents divorced, and Withers eventually moved eleven miles east, to Beckley, where he was raised primarily by his mother’s family; he was an asthmatic and a stutterer. Eager to leave West Virginia, he joined the Navy when he was seventeen, and spent nine years in the service. While stationed in Guam, he took to singing in local bars, favoring material by artists like Johnny Mathis. After settling in Los Angeles, in 1967, and landing a job installing toilets on airplanes, Withers met the trombonist and pianist Ray Jackson, who helped him make the demo that got him signed to the independent Sussex label.

Withers says that he is an untrained musician, and his songs bear him out, not because they lack sophistication but because they ignore tendencies that deserve to be ignored more often. “Ain’t No Sunshine” is a two-minute song with only three verses, a bridge that repeats two words twenty-six times—“I know”—and no chorus to speak of. Withers likes to form guitar chords that he can simply move up and down the neck without altering the position of his fingers. This simple approach leaves room for his baritone voice to map out subtle, articulate melodies. “Harlem,” the brilliant A-side that was unjustly ignored in 1971, modulates steadily upward in key in the course of its eight verses, pounding forward on a square beat that, while propulsive, sounded nothing like the R. & B. or funk of the time. As he put it, it’s “1970, 1971 or something, you know, I’m this black guy coming out sitting on a chair with an acoustic guitar.”

“Just As I Am” was an adult formation of pop, with little time for obscure metaphor or gnomic phrases. Withers’s gift lies in the immediacy of his scenarios and in how few words he needed to turn around a thought: his common explanation for how he reached conclusions as a writer is “I was feeling what I said.” His willingness to express his most awkward emotions was matched by an intolerance for unsubstantiated shows of emotion. As he told Ellis Haizlip, the host of the television show “Soul!,” in 1971, “I’m sick and tired of somebody saying ‘I love you’ with both arms up in the air like that. I can’t believe that.” Withers made his vulnerable moments as sharp as his angry moments, and his angry songs were as complex as his love songs. “Just As I Am” and its follow-up album, “Still Bill,” are as fine as any singer-songwriter albums released in the seventies.

What happened after the release of the Sussex albums is still a subject of debate, though the facts themselves are not hidden. Sussex went bankrupt, and, although Withers could have bought back his albums, CBS Records scooped up the lot for a rumored hundred thousand dollars in 1975. Withers’s relationship with CBS was, at best, fraught. The songs that he recorded for CBS were no longer about the struggles of day-to-day life; they were, mostly, the easy palliatives he had never seemed to endorse. The driving chords and stomping foot were replaced by twinkling electric pianos and lyrics about reassuring unrealities like “crystal raindrops.” This lyric is from “Just the Two of Us,” written with Ralph MacDonald and William Salter, in 1980. It became a huge hit, though in style a world away from the ascetic soul Withers started with.

After 1985, Withers stopped recording entirely. The songwriting and licensing royalties kept coming in, enough to pay the rent in Los Angeles for the past twenty-five years.

The directors of “Still Bill,” Alex Vlack and Damani Baker, found Withers at home in 2007. As Withers describes it, they “kept following me around,” generating more than three hundred and fifty hours of footage in the process. “It wasn’t like I was anxious to have somebody following me around,” he said later. “They were nice people, but after a while I was done.”

At the age of seventy-one, when many would be happily telling war stories and soaking up adulation on the revival circuit, Withers watches “Judge Judy” and rails against the record companies that both thwarted him and made him wealthy. “I have to be careful that I don’t just wallow in my own comfort,” Withers says at one point. Though the movie captures Withers criticizing the CBS A. & R. man who suggested that he cover Elvis Presley’s “In the Ghetto,” in the eighties, his fiercest riposte to the white “blaxperts” can be found in an interview filmed for the 2005 reissue of “Just As I Am.”

“You gonna tell me the history of the blues? I am the goddam blues. Look at me. Shit. I’m from West Virginia, I’m the first man in my family not to work in the coal mines, my mother scrubbed floors on her knees for a living, and you’re going to tell me about the goddam blues because you read some book written by John Hammond? Kiss my ass.”

This anger is as valuable as the unmacho bravery that allowed Withers to write “Lean on Me,” maybe the best-known ode to friendship, released in 1972. At one point in “Still Bill,” Withers says he would like “for my desperation to get louder.” Three years ago, Withers reclaimed several tapes of unreleased material from his record company. Is his desperation in there, or is it yet to be recorded? It may be enough to know that a young black man from a mining town was able to bring his songs to a world that would rather have had “the Rhythm & Blues . . . with the horns and the three chicks,” as Withers has said. If a new generation simply buys the albums that he began with, they’ll have lifelong friends. ♦