Eddie Van Halen, a guitar virtuoso whose pyrotechnic riffs and solos expanded the vocabulary of hard rock, inspired legions of headbanging imitators and propelled his band Van Halen to four turbulent decades of stadium-rock stardom, died Oct. 6. He was 65.

His death was announced on Twitter by his son, Wolfgang, who did not say where he died. Mr. Van Halen, a longtime smoker, was being treated for throat cancer, years after losing about one-third of his tongue to the disease. He had attributed his cancer diagnosis to a habit of holding a metal guitar pick in his mouth while performing.

Often ranked alongside guitar-shredding rock gods Jimi Hendrix, Eric Clapton and Jimmy Page, Mr. Van Halen developed a sound that was thunderous, bright and blazing fast. He hammered on the neck of his custom “Frankenstrat” guitar, leaned on his whammy bar to create a wailing vibrato and popularized a technique known as two-hand tapping, in which he effectively added a sixth finger to his left hand.

“That sound rearranged the DNA of rock guitar forever,” Rolling Stone magazine wrote in 2019, describing Mr. Van Halen’s two-hand method on the instrumental track “Eruption.” An aptly named 1 minute 42 second explosion of triads and power chords, “Eruption” was the kind of song that sounded, as Mr. Van Halen once put it in a description of his band’s music, like “Godzilla waking up.”

In pursuit of rock-and-roll perfection, Mr. Van Halen crossed a Gibson with a Fender to build his own guitar, and said he boiled his strings and applied surfboard wax to his pickups to obtain the right sound. To gain greater control over the recording process, he constructed a studio near his home in Los Angeles, passing it off to city inspectors as a racquetball court and christening it 5150, after a legal code applied to people who are detained for signs of a mental health crisis.

His obsessive approach to music sometimes generated conflict with his bandmates, and to some critics Van Halen seemed as much a soap opera as a rock band. Mr. Van Halen seemed to have a falling out with everyone but his brother, drummer Alex Van Halen, and battled an alcohol addiction that further strained his collaborations with David Lee Roth, the band’s charismatic original singer, and successor Sammy Hagar, a veteran rock vocalist.

In part, he said, his struggles were inherited from his father, a Dutch clarinetist he described as a fellow alcoholic. “I don’t mean to blame my dad, but when I started playing in front of people, I’d get so damn nervous,” Mr. Van Halen told Esquire magazine. “I asked him, ‘Dad, how do you do it?’ That’s when he handed me the cigarette and the drink. And I go, Oh, this is good! It works! For so long, it really did work. And I certainly didn’t do it to party. I would do blow and I would drink, and then I would go to my room and write music.”

Mr. Van Halen was born in the Netherlands but raised in Pasadena, Calif., where in 1974 he formed Van Halen with his brother as well as bassist Michael Anthony and Roth, a karate-kicking showman who added raunchy, hedonistic lyrics to Mr. Van Halen’s songs.

In an era when punk was ascendant and disco ruled the charts, Van Halen’s self-titled 1978 debut was a work of cheerfully melodic hard rock, featuring songs such as “Jamie’s Cryin’,” “Runnin’ With the Devil” and an amped-up cover of the Kinks’ “You Really Got Me.” Critics were generally dismissive, calling the band a rip-off of groups like Deep Purple and Led Zeppelin, but within a few years Van Halen was playing to sold-out arenas nationwide.

The band was credited with galvanizing a glam-rock boom, with acts seeking to imitate Mr. Van Halen’s quicksilver guitar solos and Roth’s exuberant stage antics, which included a samurai-sword dance and a split-kicking leap from the drum riser.

And like so many other groups of their era, Van Halen developed a reputation for wanton excess. A rider buried in their contract demanded that venues provide munchies, with all brown M&Ms removed from the candy bowl. (Roth later said the color restriction was a test to ensure that the band’s contract had been thoroughly read.)

While Roth presided over bacchanalia in the wings, Mr. Van Halen preferred a more private kind of debauchery, retiring alone to his hotel room to snort cocaine, drink vodka and write songs on his guitar. The self-described “quiet one in the band,” he reportedly lived with his parents until 1981, when he married actress Valerie Bertinelli of the CBS sitcom “One Day at a Time.”

Their relationship made him an increasingly public figure, as did collaborations with artists including Brian May of Queen, Roger Waters of Pink Floyd and Michael Jackson, for whom he contributed a searing, uncredited guitar solo on the 1983 single “Beat It.” Later that year, Mr. Van Halen and his band released the song that became their sole No. 1 hit, breaking through to a pop audience with the anthem “Jump.”

The song featured a synthesizer line that Mr. Van Halen had written several years earlier, much to the dismay of his bandmates. “Dave said that I was a guitar hero and I shouldn’t be playing keyboards,” he told Guitar World magazine in 2014. “My response was if I want to play a tuba or Bavarian cheese whistle, I will do it.”

In 1985, clashes between the guitarist and singer culminated with Roth’s announcement that he was leaving the band to focus on his solo career, a decision that seemed to signal the end of Van Halen. Instead, Mr. Van Halen and his remaining bandmates joined up with Hagar, a rock journeyman who had previously sung with the band Montrose.

Nicknamed Van Hagar by some fans and critics, the new lineup released four straight chart-topping studio records but fractured amid the release of the 1996 compilation album “Best of: Volume 1,” which featured two new songs recorded with Roth. During a tumultuous six-month span in that period, the band breezed through three different singers, briefly working with Gary Cherone of the Boston band Extreme.

Mr. Van Halen quipped that his group was infected by “LSD, lead singer disease.” A decade later, the band was still struggling to repair its bonds and postponed parts of a 2007 reunion tour with Roth. When they were inducted into the Rock & Roll Hall of Fame that year, only Hagar and Anthony attended the ceremony, with Mr. Van Halen having recently entered rehab.

“We accused each other of betrayal and thievery and lies and treachery,” Roth told the Los Angeles Times in 2012. “And it was all true. We were all guilty. Dig up the past, and it’s going to get all over everybody.”

By most accounts, Edward Lodewijk Van Halen was born in the Dutch city of Nijmegen on Jan. 26, 1955. The family moved to Pasadena in 1962, where his father worked as a janitor and dishwasher, playing the clarinet and saxophone at weekend gigs while encouraging his sons to pursue a career in music. His mother, a homemaker from Dutch colonial Indonesia, was more practical and suggested they find paying jobs.

Mr. Van Halen and his brother were trained on the piano before turning to rock, inspired by groups such as the Dave Clark Five and Cream, whose records Eddie slowed to a crawl to learn Clapton’s guitar solos note for note.

He had initially played the drums, making payments on his kit by working a paper route. Alex was taking guitar lessons at the time but picked up the sticks while Eddie was on the job; he soon surpassed his brother, leading them to trade instruments.

Eventually they formed a band called Mammoth, partnering with two fellow students at Pasadena City College, Anthony and Roth. The group became Van Halen in 1974, and within three years they had recorded a demo tape financed by Gene Simmons of Kiss and signed a contract with Warner Bros.

Their seminal early records included “Diver Down” (1982) and “1984” (1984), which featured “Jump” as well as the MTV standouts “Hot for Teacher” and “Panama.” It was followed by “5150” (1986), the first Hagar album and Van Halen’s first chart-topping record.

After releasing one poorly received album with Cherone, “Van Halen III” (1998), the band regrouped in 2012 with “A Different Kind of Truth.” Roth was back on vocals, but Anthony was replaced by Mr. Van Halen’s son Wolfgang, a bassist (named for Mozart) who joined the band at 15. Mr. Van Halen said it was the first time he had recorded an album sober.

His marriage to Bertinelli ended in divorce — in a memoir, she blamed drugs and infidelity on both their parts — and in 2009 he married Janie Liszewski, a publicist and former stuntwoman. A complete list of survivors was not immediately available.

In 2015, Mr. Van Halen embarked on his last major tour, joined by his brother, son and Roth, with whom he barely had a relationship. “I think it’s now built into people’s DNA, that it just won’t be Van Halen if it’s not Roth’s voice,” he told Billboard magazine by way of explanation. “You make music for people. Otherwise, just play in your closet. And how do you reach the most people? By giving them the band that they know. To do it any other way would be selfish.”