Kris Kristofferson, a singer-songwriter whose trove of country-pop hits such as “Me and Bobby McGee” and “Help Me Make It Through the Night” pushed him to the forefront of American popular composers and whose gritty-voiced, easygoing sex appeal propelled him to starring roles in Hollywood, died Sept. 28 at his home in Maui. He was 88.

A family spokeswoman, Ebie McFarland, confirmed the death but did not provide a cause.

In a musical genre known for performers with hardscrabble roots, Mr. Kristofferson stood out as an Air Force brat who developed a passion for the English Romantic poet William Blake while at Oxford on a Rhodes scholarship. He also harbored secret songwriting ambitions.

Fulfilling his family’s expectations, he spent years piloting helicopters as an Army Airborne Ranger. But in 1965, then-Capt. Kristofferson quit a promising military career to pursue songwriting in Nashville - and supported himself as a janitor at a recording studio on the city’s fabled Music Row, among other jobs. “Blake thought that if you were called by the Divine to be creative, you were obligated,” he once told the London Independent. “He said that if you buried your talent, sorrow and desperation would pursue you throughout life, and after death, shame and confuse you until eternity. For a young guy like me who wanted to be creative against everybody else’s advice, that was powerful stuff.” His marriage to his high-school sweetheart imploded. In a letter, his mother essentially disowned him. Johnny Cash, who saw in Mr. Kristofferson a kindred rebel spirit and soon became one of his ardent backers, offered a sarcastic consolation: “It’s always nice to get a letter from home, ain’t it Kris?”

Mr. Kristofferson’s persistence was legendary. He was pushing a broom when he first pitched a few songs to Cash, who turned him down. A year or two later, while working a side job as a helicopter pilot for Gulf Coast oil rigs, he borrowed a chopper and flew it to Cash’s home in the hope of making an impression.

“The truth is I almost landed on the roof of his house . . . and he wasn’t even there,” Mr. Kristofferson told the Tampa Bay Times. “His groundskeeper came out and got the tape. But John liked the story enough that he made up that I got out of the helicopter with a beer in one hand and a tape in the other.”

In short order, Mr. Kristofferson was attracting attention for his sophisticated compositions juxtaposing freedom and loneliness, romance and loss, tenderness and a degree of carnality that was groundbreaking and controversial in that era of country music.

His rugged brand of sensitivity brought him acclaim as a poet laureate of intimacy and longing. “He is the Marlboro Man with a tender heart,” arts critic Christine Arnold once wrote in the Miami Herald.

Mr. Kristofferson sang with a raw, uncultivated baritone that, coupled with his rudimentary guitar skills, was inordinately expressive and moving. His songs were marked by simple melodies, poignant details and scattered wisdom. “Me and Bobby McGee” is the tale of a drifter (“feeling nearly as faded as my jeans”) who briefly finds love with a woman on the road. The chorus declares, “Freedom’s just another word for nothin’ left to lose.”

His “Sunday Mornin’ Comin’ Down” was a masterly portrait of a man with a hangover who alternates in desperation for redemption or another pull at the bottle: “The beer I had for breakfast wasn’t bad, so I had one more for dessert. Then I fumbled through my closet, for my clothes, and found my cleanest dirty shirt.”

“The Pilgrim: Chapter 33” was a case study of a haunted renegade, based partly on Cash. “He’s a poet, he’s a picker,” Mr. Kristofferson wrote, “a pilgrim and a preacher, and a problem when he’s stoned. He’s a walkin’ contradiction, partly truth and partly fiction, takin’ ev’ry wrong direction on his lonely way back home.”

His gentle opening line in “Help Me Make It Through the Night” - “Take the ribbon from your hair, shake it loose and let it fall” - sets the scene for a sorrowful tryst: “I don’t care what’s right or wrong, I don’t try to understand, Let the devil take tomorrow, Lord tonight I need a friend.”

The song earned Mr. Kristofferson a Grammy Award for country song of the year in 1971, the first of his three Grammy wins in addition to a Grammy for lifetime achievement in 2014. In 2004, he was inducted into the Country Music Hall of Fame.

Willie Nelson once likened Mr. Kristofferson’s lyrics to great literature “whether you sing them or read them. They’re words to live by, and that’s about as much praise as you can say about any writer.”

It was ultimately a matter of time before Hollywood discovered Mr. Kristofferson, whose laconic charisma was exemplified by his deep-set blue eyes, rakish smile and full beard.

He debuted in his friend Dennis Hopper’s experimental “The Last Movie” (1971), filmed in Peru. (“All those Hollywood people in the cocaine capital of the world,” the notoriously hard-living Mr. Kristofferson recalled decades later. “It was insane.”)

He was a drug-dealing ex-pop singer in “Cisco Pike” (1972) and the next year starred as outlaw Billy in “Pat Garrett & Billy the Kid.” He played a divorced rancher who becomes Ellen Burstyn’s love interest in “Alice Doesn’t Live Here Anymore” (1974), directed by Martin Scorsese.

The role that defined his career was the ill-fated alcoholic rock star in the 1976 remake of “A Star is Born,” co-starring Barbra Streisand. He and the film were savaged by critics, but it was a box-office sensation. He also portrayed a gridiron star in “Semi-Tough” (1977) opposite Burt Reynolds and a renegade trucker in “Convoy” (1978) with Ali MacGraw, among many other parts, while simultaneously playing music to capacity crowds in arenas.

But Mr. Kristofferson’s stratospheric rise as one of the top draws in movies and music soon stalled amid a series of professional and personal traumas. First there was his starring role in the disastrous “Heaven’s Gate” (1980), a movie western plagued by massive cost overruns and off-camera conflicts.

At the same time, his second marriage, to singer-songwriter Rita Coolidge, was melting down amid what she later characterized as his emotional abuse, habit of downing two bottles of Jack Daniel’s a day, and chronic infidelity. Steamy nude scenes from a movie he made with actress Sarah Miles were reprinted in Playboy magazine, which Coolidge considered a final indignity.

Feeling “adrift” after his marriage crumbed, Mr. Kristofferson managed to curb his drinking. He eventually moved to Maui and became increasingly outspoken in liberal politics and human rights activism. Long off the country charts, he played club dates and recorded solo albums for small labels.

He began to resurrect his musical career in 1985 when he began touring with Cash, Nelson and Waylon Jennings as a supergroup called the Highwaymen. Between 1985 and 1995, they recorded three albums: two on Columbia Records and one for Liberty Records. Their Columbia works produced three chart singles, including the No. 1 “Highwayman” in 1985.

The group, dubbed “the Mount Rushmore of country music” was featured in a 2016 documentary/concert film, “The Highwaymen: Friends Till the End,” part of the PBS “American Masters” series. In the film, Mr. Kristofferson offered the following descriptions of his fellow musicians: “Willie’s the outlaw coyote. Waylon’s the riverboat gambler. I’m the revolutionary communist radical, and John is the father of our country.”

He later took a range of supporting acting parts and was compelling as a racist sheriff in filmmaker John Sayles’s border town drama “Lone Star” (1996). He also played a vampire-hunter named Whistler in the “Blade” franchise. Mr. Kristofferson once told the Herald that he had no great drive to become a Hollywood star.

“I was really trying for a while just to experience as much as I could because I wanted to be a writer,” he said. “You know, Jack London held every job there was. And I tried to. It’s terrific for what I do. The task of portraying somebody is a lot easier if you’ve been a lot of different people.”

Kristoffer Kristofferson, his first name reflecting his partial Swedish heritage, was born in Brownsville, Tex., on June 22, 1936. His father, then in the Army Air Corps, became an Air Force major general. His mother was a homemaker. He grew up drawn to the unvarnished, emotional vocals of Hank Williams and wrote his first tune at 11, a Williams-inspired ditty he called “I Hate Your Ugly Face.” He completed high school in San Mateo, Calif. While at California’s Pomona College, he earned two prizes in a national collegiate short story competition sponsored by the Atlantic Monthly. He also became a Golden Gloves boxer and made the Phi Beta Kappa academic honor society while serving as an Army ROTC commander.

He graduated from Pomona in 1958 and, on a Rhodes scholarship, pursued his studies on Blake while struggling to write novels. In 1960, he left Oxford without a degree and soon married his high school girlfriend, Frances Beer, and joined the Army as a commissioned officer.

While stationed in Germany, Mr. Kristofferson began to rebel against the trajectory of his life. He drank heavily and wrecked cars and motorcycles. Seeking greater adventure, he volunteered for Vietnam, only to discover his next assignment would be teaching English at the U.S. Military Academy at West Point.

His platoon leader, impressed by Mr. Kristofferson’s songs, connected him with an aunt, country songwriter Marijohn Wilkin. Her encouragement led Mr. Kristofferson to visit Nashville in July 1965 for a two-week leave that decided his future.

The next year, he wrote “Vietnam Blues,” a stinging rebuke of antiwar protesters that became a top-20 country single for singer Dave Dudley. (The song reflected Mr. Kristofferson’s rightward political leanings before his beliefs took a hard left turn, the result of talking to friends who served in Vietnam.)

Janis Joplin, with whom the songwriter had a brief affair, recorded “Me and Bobby McGee,” days before her death in 1970 from a heroin overdose at 27. Released in 1971, it became her only No. 1 single.

In 1970, the year Monument Records released Mr. Kristofferson’s first album, three of his songs, including Cash’s interpretation of “Sunday Mornin’ Comin’ Down,” became No. 1 country singles. Ray Price’s aching performance of the bittersweet breakup lament “For the Good Times” also became a pop hit. Sammi Smith’s sensual rendering of “Help Me Make It Through the Night” became her signature.

His most successful year as a recording artist was 1973. Inspired by a visit to Nashville’s Evangel Temple, pastored by the son of country legend Hank Snow, he wrote and recorded the simple, eloquent gospel ballad “Why Me,” his only No. 1 country single. He and Wilkin co-wrote the modern gospel standard “One Day At a Time.” He and Coolidge shared a Grammy for their duet on Mr. Kristofferson’s dissolute, pessimistic “From the Bottle to the Bottom.”

From 2004 to 2015, Mr. Kristofferson experienced progressive memory loss. Doctors told hin that the worsening condition was caused by either by Alzheimer’s or by dementia that was brought on by blows to the head he suffered in his athletic youth.

He said in an interview with Rolling Stone Country that it got so bad, he sometimes couldn’t remember what he was doing from one moment to the next.

In 2016, a doctor decided to test Kristofferson for Lyme disease, which came back positive. It was possible he picked it up years ago in Vermont for six weeks while filming the 2007 movie “Disappearances.”

In addition to his third wife, Lisa Meyers, with whom he had five children, survivors include two children from his first marriage; a daughter from his second marriage; and seven grandchildren.

Mr. Kristofferson was inducted into the Songwriters Hall of Fame in 1985 and the Country Music Hall of Fame in 2004. At a 2015 ceremony sponsored by a music industry charity, singer-songwriter Bob Dylan described Mr. Kristofferson’s early impact on staid, traditionalist Nashville.

“Everything was all right until - until - Kristofferson came to town,” he said. “Oh, they ain’t seen anybody like him. He came into town like a wildcat that he was, flew a helicopter into Johnny Cash’s backyard, not your typical songwriter. And he went for the throat.”

Adam Bernstein contributed to this report.