Jim Ladd, the pioneering and hugely popular freeform rock-radio DJ, has died. The Los Angeles Times reports that Ladd died at home in Carmichael, California on Saturday. He’d suffered from a heart attack. His SiriusXMU colleague Meg Griffin announced Ladd’s passing on his Deep Tracks show last night. Ladd was 75.

Jim Ladd was one of the DJs who took true advantage of the relaxed rules on FM radio in the late ’60s. Before a 1964 FCC ruling, FM stations would simply simulcast everything that was played on the owners’ more-popular AM stations, but the FCC said that FM stations had to include at least 50% original material. This led to a surge in demand for cheap FM-radio programming, and DJs like Ladd rushed in to fill that demand. FM DJs would choose their own playlists, spinning deep cuts rather than singles and sometimes espousing anti-establishment views. Ladd, who called himself the Lonesome LA Cowboy, might’ve been the most famous of them.

When he was barely out of his teens, Jim Ladd started his career on the Long Beach rock station KNAC. After stints on KNAC and KLOS, Ladd moved to the LA station KMET in 1974, and he mostly stayed with that station until it switched to a new age format in 1967. During his time at KMET, Ladd built a large following and a reputation for refusing his bosses demands to hew to pre-planned playlists. On his syndicated show Innerview, Ladd welcomed guests like John Lennon, Joni Mitchell, and Led Zeppelin.

After losing his KMET job, Jim Ladd played the DJ on Pink Floyd member Roger Waters’ 1987 solo album Radio K.A.O.S. He toured with Waters and acted in the album’s music videos. Ladd also played radio DJs in films like Say Anything, She’s Gotta Have It, and Tequila Sunrise. He inspired Tom Petty’s 2002 album The Last DJ and its title track.

In his later career, Ladd worked stints at other radio stations and published the 1991 book Radio Waves: Life And Revolution On The FM Dial. He received a star on the Hollywood Walk Of Fame in 2005, and he started working at Sirius in 2011, keeping that post until his death.