Claire Bates (Melinda Page Hamilton) is the main villainess from "The Instincts," episode 4.06 of Criminal Minds (airdate November 5, 2008).
Not much is revealed about Claire's backstory other than a history of psychotic and violent behavior. She was arrested and institutionalized in 2004 for attacking a secretary at her workplace, with the incident including Claire biting off a part of her victim's ear. Her only (mentioned) relative was her father, Herbert Evans, who passed away two years prior to the events, and she had been living in his home in Reno, Nevada. In early 2008, Claire became pregnant and went off her anti-psychotic medication to make sure her baby (a boy) was healthy.
Claire gave birth to her son, but a week later, she lost custody of her son after Child Services deemed her an unfit parent. After losing her son, Claire believed that her son had died a week after birth, and her delusional belief led her to become a kidnapper, with her first victim being five-year-old Ethan Hayes. The deranged psychopath kept took care of Ethan by breastfeeding him, believing that he was an infant (her "deceased" infant son) rather than a developed child. After a week of taking care of Ethan, Claire smothered him to death with a pillow, doing so to recreate the "death" of her son.
After killing Ethan, the evil Claire abducted four-year-old Michael Bridges, the only son of Amy and Craig Bridges, which brought BAU on the case. While holding Michael captive, the villainess taunted the couple--mainly Amy--anonymously, stating that Amy was a bad mother and that Michael was happier with her, even adding that Ethan was better off with her than with his own parents. In an attempt to draw out Michael's kidnapper, the couple and BAU attended Ethan's funeral, with Claire also attending. However, the group arrested a man named Walter Davis under their suspicion, and afterwards, Claire contacted Aaron Hotchner and revealed her knowledge of him and the group being at the funeral, with the call being interrupted by Amy's demand to see Michael.
Spencer Reid's intuition that the abductor had a delusional belief that their victim was a newborn led to Claire being revealed as the culprit, and after Claire was shown breastfeeding Michael, the deranged villainess went outside the house and built a fire; dousing logs with gasoline. The BAU arrived and caught Claire with a blanket, leading them to believe that she had Michael and chasing her to the site of the fire. In response to the BAU's pleas to put down who they believed was Michael, Claire constantly fretted over her son, who she claimed was dead, only for Emily Prentiss to state that he was being taken care of by a new family. Regarding Michael, he was still inside the house and rescued by Reid, and what Claire later threw into the fire was revealed to be toys that were meant for her actual son. With the ordeal over, Claire was handcuffed and arrested for the abductions and for Ethan's murder.