William and Diana Reid originally had a good marriage in Las Vegas, in spite of her paranoid schizophrenia. They had a son, named Spencer, together. William wanted to have more children, but Diana didn't approve. He would, however, coach a local little league baseball team. In 1984, a young boy, Riley Jenkins, was raped and murdered. The investigation led nowhere and the killer went free. Not long afterwards, Gary Michaels, the killer, began stalking Spencer, even playing chess with him. Diana, who saw Michaels for what he was, told about him to Riley's father, Lou Jenkins. She later found herself in his car on his way to Gary, who was beaten to death by Lou. Since she got blood on her clothes, William helped her dispose of them by burning them in the yard. As a result of the incident, the Reids' marriage deteriorated and William left Diana and Spencer. He still lived in Las Vegas and continued working as an attorney at the Kierschenbaum, Wieder and Moore law firm in Summerlin, keeping tabs on Spencer's career in the BAU. They remained estranged, with Spencer being oblivious as to his whereabouts.
On Criminal MindsEdit
During a series of child abductions in the same area, Spencer keeps having dreams related to Riley's murder. After the case is closed, he has another dream, in which he sees William in a basement with the body, prompting him to investigate the murder with him as a suspect. After he finds out that the real killer was Gary, Diana and William come forward and tell him the truth about what happened. William presumably went back to his regular life afterwards.
- It was mentioned in Memoriam that he had a very sick cat, drives a 2005 Toyota Prius hybrid, and his favorite author is Isaac Asimov.
- According to the bank statements, he lives at 3110 Knoll Avenue in Las Vegas, NV 89167.
- When he was packing his bags to leave in the flashback scene in Revelations, his excuse was that he couldn't help Diana if she couldn't take care of herself. He also refused to take Spencer with him, even though Diana asked him to - if only for a few days.
- He claimed he didn't go back to his family because he "didn't know how to be a father" to Spencer "anymore".