Billy Chenowith is a recurring character who is the son of Bernard Chenowith and Margaret Chenowith and the younger brother of Brenda Chenowith. He was portrayed by Jeremy Sisto.


He and Brenda had a close relationship as children but he was diagnosed with bipolar disorder and hospitalized.  When released, he showed up at her house unnanounced and later attacked her, attempting to give her a tattoo in honor of a book character they both liked as children.

He was previously in a relationship with Olivier Castro-Staal, who taught him art at college. He meets Claire Fisher in 2001 and the two later become an item but he ceases taking his medication, thus becoming more unstable, which leads to Claire breaking up with him for her own safety. He pleads with her to take him back but she refuses, even though he goes back on his medication.

When Brenda dies, he is shown by her side talking to the doctor.


  • Although absent for the first three episodes of the first season despite having an uncredited role in the pilot, Billy did not become a series regular until the fourth episode.