Billy Chenowith

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.

History
He and Brenda had a close relationship as children but he was later diagnosed with bipolar disorder and hospitalized. When released, he showed up at her house unannounced and later attacked her after cutting off his own tattoo and wanting to cut off her matching tattoo, which were the names of literary characters from a children's book.

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 her 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 complaining about his (now long gone) relationship with Claire.

Trivia

 * 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.