Glen Campbell, a guitar prodigy and ballad singer who dominated the polished, string-swelling countrypolitan sound of the late 1960s and 1970s and cultivated a clean-cut image at odds with his once-stormy personal life, died Aug. 8 in Nashville. He was 81.

His publicist confirmed the death to the Associated Press. Mr. Campbell announced that he had Alzheimer’s disease in 2011 and performed what he called the Glen Campbell Goodbye Tour shortly thereafter. In 2015, he won his sixth and final Grammy Award, honored for best country song “I’m Not Gonna Miss You,” which he co-wrote for a documentary about his life and deteriorating health.

In a career that spanned six decades, Mr. Campbell made dozens of albums, sold more than 40 million records and was inducted into the Country Music Hall of Fame. At a time when the grittier “outlaw” movement of Waylon Jennings and Willie Nelson was on the rise, Mr. Campbell vaulted to fame as an unabashed sentimentalist whose songs were aimed squarely at the American heartland.

His best-known recordings included John Hartford’s “Gentle on My Mind” (which became his theme song) and Larry Weiss’s “Rhinestone Cowboy.” His most frequent collaborator was songwriter Jimmy Webb, who provided expressive, wistful hits such as “By the Time I Get to Phoenix,” “Galveston” and “Wichita Lineman.”

“My approach is simplicity,” Mr. Campbell told Time magazine in 1969. “If I can just make a forty-year-old housewife put down her dish towel and say ‘Oh!’ — why then, man, I’ve got it made.”

1 of 19 Full Screen Autoplay Close Skip Ad × Remembering superstar entertainer Glen Campbell (1936-2017) View Photos Glen Campbell, the grinning, high-pitched entertainer whose dozens of hit singles included “Rhinestone Cowboy” and “Wichita Lineman” and whose appeal spanned country, pop, television and movies, died on Aug. 8, 2017, his family said. He was 81. Caption Glen Campbell, the grinning, high-pitched entertainer whose dozens of hit singles included “Rhinestone Cowboy” and “Wichita Lineman” and whose appeal spanned country, pop, television and movies, died on Aug. 8, 2017, his family said. He was 81. 1987 Country star Glen Campbell plays the guitar during a performance. Campbell, a guitar prodigy and ballad singer who dominated the polished, string-swelling countrypolitan sound of the late 1960s and 1970s and cultivated a clean-cut image at odds with his once-stormy personal life, died at 81 in Nashville. AP Buy Photo Wait 1 second to continue.

Mr. Campbell was 4 when an uncle bought him a $5 mail-order guitar from a Sears, Roebuck & Co. catalogue. He taught himself to play as an escape from sharecropping, explaining, “Picking a guitar was a lot easier than picking cotton.” He grew to admire the Belgian-born jazz guitarist Django Reinhardt, whom he called “the most awesome player I ever heard.”

Without any formal training, Mr. Campbell became by the early 1960s part of the Wrecking Crew of Los Angeles, studio musicians who were known for their versatility and skill.

He played rhythm guitar on more than 500 jazz, pop, rock and country records, backing entertainers such as Frank Sinatra, Nat “King” Cole, Elvis Presley, Merle Haggard and the Beach Boys. When Beach Boy Brian Wilson had a breakdown in 1965, the band asked Mr. Campbell to fill in on tour. Singing falsetto and playing bass, he got his first taste of crowd frenzy.

“Right after one concert,” he told the New York Times, “the Beach Boys ran for the cars like mad, but I didn’t care. I took my time, figuring nobody would pay any attention to me, since I wasn’t really a Beach Boy. Well, I want to tell you, they jumped on me with all four feet — started yankin’ my hair, stole my watch, tore off my shirt. From then on, I was the first one in the car.”

Mr. Campbell broke through as a solo act in 1967 with a flurry of Grammy Awards for “Gentle on My Mind.” Strapping, clean-cut, farm-boy handsome and with an easygoing charisma, he was soon in demand as a television guest star.

Through a friendship with comedian Tommy Smothers, Mr. Campbell co-hosted “The Summer Brothers Smothers Show” on CBS in 1968. He acquitted himself so smoothly — despite his aversion to the program’s liberal politics — that the network hired Mr. Campbell to host a variety show, “The Glen Campbell Goodtime Hour,” which aired from 1969 to 1972.

He also was cast as a supporting actor in the John Wayne movie “True Grit” (1969), whose theme song he sang.

In interviews, he could be quick-witted and charming, tossing off one-liners and country-fried quips.

On his upbringing in rural Arkansas: “If we grew it, we ate it. If Daddy shot it, Mamma cooked it.” On his vault to movie, TV and record fame in the late 1960s: “Woooowheee! Ah been busier than a three-headed woodpecker!” On his movie role: “ ‘True Grit’ was fun to do, but I wasn’t cut out to be an actor. I made John Wayne look so good, he won his only Oscar.”

Mr. Campbell remained a top country act for many more years. “Rhinestone Cowboy” brought him a No. 1 country and pop hit in 1975, and he duplicated that success in 1977 with the rollicking and infectious “Southern Nights,” written by Allen Toussaint.

Mr. Campbell said the demands of celebrity and a series of troubled marriages led to his prodigious drinking and cocaine use. “I didn’t hold back in those days,” he later told the London Independent, recalling how he trashed hotel suites and got into other messes.

There was a time, he said, that he boarded a plane, got into a seating dispute with an Indonesian government official and drunkenly told the man he would “call my friend Ronald Reagan and ask him to bomb Jakarta.”

His most-chronicled escapade was his tumultuous relationship with country and pop singer Tanya Tucker, who projected a wildcat, man-eating persona and, at 22, was half Mr. Campbell’s age.

They performed the national anthem together at the 1980 Republican National Convention. The next year, their tawdry row outside a hotel near Shreveport, La., attracted the attention of local authorities and then the media. It was not the last time their differences surfaced loudly and publicly.

In 1982, Mr. Campbell wed his fourth wife. He announced he was a born-again Christian and that he had given up drugs and drinking. He had a relapse in 2003, when he was arrested for a hit-and-run incident in Phoenix after plowing his BMW into another car. He later pleaded guilty to drunken driving and was sentenced to 10 days in prison.

His police mug shot — looking zoned out, craggy and unkempt — became a public sensation on the Internet. He vowed never to touch alcohol again. His musical reputation had survived more than intact, and, in 2005, he was named to the Country Music Hall of Fame.

That year, he joked that he couldn’t imagine he was in any hall of fame.

“They could never put me in a slot,” he told the Chicago Sun-Times. “They couldn’t say Glen was ‘country,’ ‘pop’ or ‘rock.’ I’m crock, OK? A cross between country and rock. Call me crock.”

Glen Travis Campbell was born on April 22, 1936, in Delight, Ark., and grew up on a family farm with 11 siblings. He played guitar at church picnics, on local radio shows and at nightclubs in cities as far away as Houston by the time he left school in 10th grade to perform full-time with an uncle’s Albuquerque-based country band.

In the late 1950s, Mr. Campbell started his own Western combo and, encouraged by the positive reaction, decamped for Hollywood in the hope of a major solo career. He wound up as a session player, backing up other stars in the music studio.

He played on Sinatra’s “Strangers in the Night,” the Righteous Brothers’ “You’ve Lost That Lovin’ Feelin’,” the Beach Boys’ “Pet Sounds” album and the Monkees’ “I’m a Believer.”

He bonded with Presley while recording the “Viva Las Vegas” soundtrack. “Elvis and I were brought up the same humble way — picking cotton and looking at the north end of a southbound mule,” he once quipped.

The session work was profitable for Mr. Campbell, but he felt he was delaying his ambitions. He had a minor hit as a singer with the 1961 pop single “Turn Around, Look At Me.” But he did not fully emerge as a headliner until recording “Gentle on My Mind” in Nashville. Soon came “The Glen Campbell Goodtime Hour,” with Steve Martin and Rob Reiner among the writers.

His marriages to Diane Kirk, Billie Jean Nunley and Sarah Barg Davis — the former wife of singer Mac Davis — ended in divorce. In 1982, he wed Kimberly Woolen, a dancer at Radio City Music Hall in New York.

A complete list of survivors could not be immediately confirmed.

After his final marriage, he turned out gospel and devotional music while also maintaining a steady outpouring of country music that included Top-10 hits such as “I Have You” (1988) and “She’s Gone, Gone, Gone” (1989). In 1994, he published a memoir, “Rhinestone Cowboy,” written with Tom Carter.

The singer drew fresh critical attention for “Meet Glen Campbell” (2008), a recording session that included covers of songs by such disparate rock bands as Green Day, U2 and the Velvet Underground. He followed with the well-received “Ghost on the Canvas” in 2011, featuring admirers such as Smashing Pumpkins guitarist Billy Corgan and Cheap Trick guitarist Rick Nielsen.

The next year, Mr. Campbell received a Grammy Award for lifetime achievement, and he continued to record new music despite his failing health.

“I don’t know if I got it,” he told the Chicago Tribune, referring to Alzheimer’s. “That’s what the doctor said, but I don’t know what it is. I said, ‘I’m going to go on and live my life. And to heck with that.’ ”