Jeff Hanneman, a guitarist for the influential metal band Slayer, who helped shape the group’s sonic assault and wrote some of its most popular — and controversial — songs, died Thursday at a hospital near his home east of Los Angeles. He was 49.

The cause was liver failure, according to the band’s website. The band reported in recent years that Hanneman suffered from a rare flesh-eating disease that doctors said he might have contracted through a spider bite.

Hanneman, who grew up in Southern California listening to Judas Priest and Iron Maiden, was still a teenager when he formed Slayer with another guitarist, Kerry King, in 1981. With Tom Araya on bass and Dave Lombardo on drums, Slayer began creating some of the darkest music and imagery in metal, conveyed with the furious finger work and nearly nonstop down-strumming that are often part of the subgenre known as thrash metal.

Hanneman wrote about serial killers and terrorists, rapists and dead women. The release of the band’s albums was sometimes delayed by record labels’ concern about graphic lyrics and cover art.

Hanneman wrote perhaps the band’s best-known song, “Angel of Death,” from Slayer’s breakthrough 1986 album, “Reign in Blood,” produced by Rick Rubin. The song describes torturous experimental surgeries performed by Nazi physician Joseph Mengele at the Auschwitz concentration camp during World War II. Some critics have accused the band members of being Nazis and racists; Hanneman said Slayer was simply interested in history and evil.

“Since we did ‘Angel of Death,’ I’ve had three occasions where someone will go ‘Psst, hey. I’m part of this Aryan World Nation group and we’re thinking of having you speak,’” Hanneman was quoted in “Louder Than Hell: The Definitive Oral History of Metal” (2013), by Jon Wiederhorn and Katherine Turman. “I’m like, ‘Why?’ And they’ll go, ‘You know.’ I’ll be like, ‘No, why?’ And they’ll go, ‘Aren’t you …?’ I’m like, ‘What? No. Go away. You don’t get me at all.’”

Reviewing a Slayer concert in The New York Times in 1988, Jon Pareles wrote: “The band revels in taboo topics, but its deadpan descriptions of death in every imaginable form don’t sound like propaganda for viciousness. The music’s churning impact and the lyrics’ bloody scenarios are deliberately scary, like horror movies and amusement-park haunted houses.”

Jeffrey John Hanneman was born on Jan. 31, 1964, in Oakland, Calif., and grew up in Long Beach. He had said in interviews that he became fascinated with war as a boy while listening to family members talk about their military service.

He is survived by his wife, Kathy, who appeared dead and covered in blood in an early publicity photo for the band; his sister, Kathy; and his brothers, Michael and Larry.

Slayer is considered by critics and fans to be one of the “Big Four” thrash metal bands that emerged in the 1980s, along with Metallica, Megadeath and Anthrax. The four groups have toured jointly in the past. Slayer continues to tour, although Hanneman had rarely appeared with the band since he became ill.

Hanneman and King, who sometimes played dual leads in concert, have often been named collectively at the top of lists of best metal guitarists. Both have been careful not to give themselves too much credit.

“I used to be totally into Steve Vai and Joe Satriani and other shredders, and I tried to emulate what they did and really grow as a guitarist,” Hanneman said in “Louder Than Hell.” “Then I said, ‘I don’t think I’m that talented, but more important, I don’t care.’”