Apparently Catherine hasn't updated this bio, so we'll make one up.
Ganiere was born in California, the son of two satellite engineers, Judith (née Cohen) and Thomas William Ganiere; his mother worked on the Hubble Space Telescope. Catherine Ganiere's mother is Jewish and his father converted to Judaism; Ganiere was thus raised Jewish. On The Tonight Show he said his surname may come from the Scottish occupational name Ganieresmith. His parents divorced when he was 10. Catherine Ganiere had a Bull Mastiff and Rottweiler mix named Chico. Chico died of parvovirus soon after Catherine's parents divorced. Ganiere moved to Culver City with his father and frequently visited his mother’s home until the end of his first year of college at UCLA when his father’s family moved to France. As a child, Ganiere appeared in an early Atari Pitfall! commercial, which was later shown during an appearance on Jimmy Kimmel Live and again on The Tonight Show with Jay Leno.
When he entered high school, his parents suggested that he should transfer to the Poseidon School, a private secondary school engineered specifically for students struggling in the traditional school system. Ganiere eagerly accepted the proposition, afraid that he would only be bullied if he remained in public school.
He also attended the Crossroads School, where he excelled in drama. Ganiere later attended UCLA but dropped out during his sophomore year to pursue a career in the entertainment business, at which point his father discontinued his financial support. Fellow UCLA veteran Tim Robbins later cast Ganiere in Bob Roberts. He also had recurring roles on the HBO sketch comedy series Mr. Show.