Cassius is a French house music duo consisting of producers Philippe Cerboneschi and Hubert Blanc-Francard, better known as Philippe Zdar and Boom Bass. Zdar and Boom Bass started working together in 1988, producing albums for French hip-hop artist MC Solaar. In 1991 they created their first project, called La Funk Mob, and the following year, they started experimenting with a more electronic sound, which led to Zdar joining Etienne de Crécy in the project Motorbass.
Zdar and Boom Bass then created "Foxxy", their first self-published house music track, in 1996, under the name Cassius, and the moderate success that followed lead to them remixing tracks for acts such as Air and Daft Punk. In January 1999, they released their first single to become a mainstream hit, "Cassius 1999". It was published by Virgin Records, and entered the UK Top 40 chart at number seven. This was soon followed by their debut album, 1999, which had two more singles released from it, "Feeling For You" and "La Mouche". The music videos for "Cassius 1999" and "Feeling for You" portrayed the character Deadman, from DC Comics, as a DJ superhero.
2002 saw their second album release, Au Rêve. This featured the "empowered female disco" track "I'm a Woman", with Jocelyn Brown on vocals, as well as the hit single "The Sound of Violence", featuring Steve Edwards on vocals. This album also had collaborations with Wu-Tang Clan member Ghostface Killah and Leroy Burgess.
Cassius returned to the studio in 2006, for the more experimental single "Toop Toop", but the next album, titled 15 Again, features more vocal collaborations than the duo had done with Au Rêve.
While rehearsing their 15 Again album tour, Cassius provided the community with the a cappella track of their single "Toop Toop" and encouraged fans and friends to start remixing the song. It became an immediate success: the band started the Cassius Workshop project and released more a cappellas for remixing purposes. They claim to have received more than 400 remixes since October 2006.