Dr. Claire Foster was a renowned psychiatrist that had Lex Luthor as a patient and a recurring antagonist in the Third Season of Smallville.
She was portrayed by the late Lorena Gale.
Following Lex Luthor's return to civilization after being stranded alone on an island, Foster was hired by Lionel Luthor to provide Lex with psychiatric care. Dr. Foster was mentioned by name as the psychiatrist with whom Lex would meet with.
Lex had met with Dr. Foster four times and was finishing up his last session with her, talking about the art in the castle and claimed that he has no emotional issues. Dr. Foster refused to sign off on Lex's mental health, recommending continuing sessions on an indefinite basis. Much to Lex's fury, she maintained that he has yet to deal with any of his emotional or physical trauma. Lex seemed to know that she was right, but he is still upset and threw her out. After an outburst towards Perry White, Lex agreed to more sessions.
Lex told Claire of his time on the island and of the apparition of Louis Leery that tormented him during his isolation. Dr. Foster promised that their sessions were confidential , but called Lionel to inform him of her discovery.
Seeing as he was close to discovering the truth about his grandparents, Lionel paid Dr. Foster to drug Lex until he seemed to be having a psychotic break. When Lex believed assassins were after him, Clark and he returned to the mansion to search for clues, when Dr. Foster arrived and tried to convince Lex that he was having a psychotic break. Lex refused to believe her and grabbed a gun and backed out admitting that he might be crazy, but he has also guessed that his father might have drugged him in order to discredit him. Lex went to confront Morgan Edge and when he was almost ran over, Clark pushed Lex out of the way and destroys the car, with Lex witnessing his powers. Clark super speeds away just as Dr. Foster arrives with some men who haul Lex away as he screams for Clark.
Dr. Foster had Lex committed to Belle Reve Sanitarium where she continued a drug regime designed to erase his short term memory. He is unhappy that his son has been in in Belle Reve for an entire month with no results. After a month, Lex still hadn't forgotten, so Lionel insisted that Dr. Foster administer radical shock therapy. She was reluctant as she had other patients who were badly injured during the treatment.