Paul Kantner, a founding member of Jefferson Airplane, died Thursday of multiple organ failure, his publicist told the San Francisco Chronicle. He was 74.

Kantner had suffered a heart attack earlier in the week. He had also suffered a heart attack in March 2015.

Paul Lorin Kantner was born on March 17, 1941, in San Francisco.His father sent him to a boarding school when he was eight following the death of his mother, leading Kantner to distrust authority at a young age and sparking a love of protest music.

Kantner broke into the business in the early 1960s as a folk musician who idolized Pete Seeger. He was the first band member recruited by Marty Balin to form Jefferson Airplane in San Francisco in 1965 after Balin saw Kantner perform at the folk club The Drinking Gourd.

The band pioneered the psychedelic sound by combining folk, rock and blues, mixing in reverb and fuzzy guitar lines. The Airplane became the first San Francisco rock group of that era to achieve mainstream success.

Jefferson Airplane’s debut show was on Aug. 13, 1965, at San Francisco’s The Matrix nightclub, which Balin had converted into a music outlet from a pizza parlor. Their first album “The Jefferson Airplane Takes Off” was released a year later to little acclaim despite Balin’s memorable “It’s No Secret.”

In 1966, singer Grace Slick replaced Signe Toly Anderson, who had left the group to start a family. Slick’s powerful vocals gave the group a defining sound and enhanced their stage presence. Their second record album “Surrealistic Pillow” — released in February 1967  — became a blockbuster success during the “Summer of Love” with the hit songs “Somebody to Love” and “White Rabbit.”

The album cover for “Surrealistic Pillow” was a simple Herb Greene black and white photo of the band with only Slick smiling. Kantner was front and center in the shot, holding a violin, and the record featured unique tracks such as “She Has Funny Cars,” “Today,” “Plastic Fantastic Lover,” “Embryonic Journey,” “D.C.B.A. – 25” and “3/5 of  a Mile in 10 Seconds.”

Kantner admitted that “D.C.B.A. 25,” which he wrote, was a reference to LSD-25. “It’s basically an LSD-inspired romp through consciousness,” he added.

Kantner was a singer and rythym guitarist in the group’s most notable lineup, which lasted three years, with co-lead singers Slick and Balin, lead guitarist Jorma Kaukonen, drummer Spencer Dryden and bass player Jack Casady.

The Airplane was the first headline act booked by Bill Graham when he opened the iconic Fillmore Auditorium in 1966. Graham managed the group for about a year, starting in early 1967. The band played at the Human Be-In at Golden Gate Park in 1967 and the Monterey, Woodstock and Altamont festivals.

Balin was knocked unconscious in a scuffle on stage by a Hells Angel at Altamont, a moment captured in the 1970 documentary “Gimme Shelter.” Kantner responded by saying sarcastically, “Hey, man, I’d like to mention that the Hells Angels just smashed Marty Balin in the face, and knocked him out for a bit. I’d like to thank you for that.”

The Airplane released four more albums — “After Bathing at Baxters,” “Crown of Creation,” “Bless Its Pointed Little Head” and “Volunteers” — before the band began to dissolve due to internal discord.

Kantner and Slick transformed the band into Jefferson Starship in the early ’70s with the album “Blows Against the Empire” while Kaukonen and Casady formed Hot Tuna. Kantner quit the group in 1984 but rejoined it in 1992 and continued to play with them until his death.

The Jefferson Airplane was inducted into the Rock and Roll Hall of Fame in 1996. “Their heady psychedelia, combustible group dynamic and adventuresome live shows made them one of the defining bands of the era,” their entry on the Hall of Fame website reads.

Kantner is survived by sons Gareth and Alexander and daughter China. Funeral arrangements are pending.

A posting on the Facebook page for The Doors said, “Our condolences go out to the friends, family and fans of Paul Kantner of Jefferson Airplane on the news of his passing. Music would not be the same without the sounds of The Doors and Jefferson Airplane, which both contributed so heavily to the signature sound of the 60s and 70s. They often shared the same bill.”

“Paul was a key architect in the development of what became known as the San Francisco Sound,” said Neil Portnow, president and CEO of the Recording Academy. “The music community has lost a true icon and we share our deepest condolences with Paul’s family and friends and with those who had the privilege of collaborating with him.”