As a teenager, Royer began his music career as a formative member of
Social Distortion with
Mike Ness and the band's original drummer. In high school, Mike Ness spent time at Royer's family home in Fullerton, where Royer created the name "Social Distortion" for the band, and began to recruit members to play. In addition to forming and naming the band, Royer wrote "Mommy's Little Monster" and composed the group's early lyrics with occasional help from original lead vocalist Tom Corvin. He later drummed with the Detours, and after parting ways with Ness, Royer became the lead vocalist of a Social Distortion splinter group before disbanding it to drum for the Adolescents on and off between 1980 and 1987. Royer wrote the song "
Amoeba" with Rikk Agnew. Royer said he got the inspiration for Amoeba during his high school science class. The song has been featured in films and video games, such as Tony Hawk's Pro Skater 3 (2001), Grand Theft Auto V (2013) and Call of Duty: Black Ops Cold War (2020), SLC Punk, The Carrie Diaries, and more. In 2009, Mark Hoppus and Travis Barker of Blink-182 covered "Amoeba" for the soundtrack to the film Endless Bummer. After the Adolescents' first break-up in 1981, Casey formed
D.I., where he is the lead vocalist, primary songwriter and only consistent member. He wrote "Richard Hung Himself", which has been covered by other artists, including Slayer. In 1983, the cult film
Suburbia was released, which features live footage of Royer and D.I. performing "Richard Hung Himself". Director
Penelope Spheeris recruited street youths and punk-rock musicians to represent each role rather than hiring actors. To pay homage to the punk rock film, which put D.I. at the helm of the American Hardcore music scene, Royer got a T.R. (The Rejected) tattoo on his arm. When the Adolescents reformed in 1986, Casey returned to the band but left before the 1987 reunion album
Brats in Battalions was recorded. He rejoined them again in 2001–02 for their 20th Anniversary Tour. Casey also joined former Adolescents band members in the band ADZ from 1989–93, after which he again made D.I. his primary focus. He has been the only constant member through many D.I. line-up shifts since the band's inception. Due to creative differences, Adolescents founders Tony, Frank and Steve kicked out Blue Album line-up members Casey Royer and
Rikk Agnew. Casey wrote a popular song on the Blue album titled "Amoeba", now considered a punk rock anthem. Steve, Tony, Frank, and Rikk shared songwriting credits for the rest of the Blue Album, creating the iconic Orange County sound recognized worldwide. In 2017, Casey and Rikk formed a Blue Album tribute band called the RADolescents with other former alumni of the Adolescents, including Rikk's young nephew Frank Jr. on vocals. Royer was recognized by the County of Orange for pioneering the early punk rock scene in Orange County. With the onset of social media, his bands are seeing a popular resurgence across the globe. As his popularity continues to increase, he was asked to be a guest tour guide at the first-of-its-kind Punk Rock Museum in Las Vegas, owned by his longtime friend
Fat Mike of punk band
NOFX. Fat Mike of NOFX says it was seeing Royer perform when he was a teenager that inspired his own punk rock career.
Noodles from the rock band
The Offspring also cites D.I. and Royer as musical inspiration, as the two bands appeared on billings together during The Offspring's early musical career. ==Personal life==