Who is Roy from A Million Little Pieces and what is their importance?

Roy is another patient on Sawyer Unit at the Clinic, one whose seniority makes him feel comfortable bullying James. He threatens to have James kicked out of the Clinic, fouls the bathroom that James must clean, and lies about it to Ken and Lincoln. After his discharge from the Clinic, he returns one night in a psychotic episode and attacks Lincoln with a cudgel. Roy, as it turns out, suffers from Multiple Personality Disorder. There is little sympathy among the other patients.