Dr. Janice Lester is the villain of "Turnabout Intruder", the final episode of the original Star Trek series, which would also make her the series' final antagonist. She was played by Sandra Smith while in her own body and by William Shatner while in Kirk's body. Lester is likely a psychopath, given her apparent lack of remorse for murdering her expedition and willingness to commit further murders. However, she was unable to kill Kirk due to still having feelings for him.