A Starfleet psychiatrist whose exposure to the galactic barrier gave her the same powers as Gary Mitchell, before she turned against him.
Elizabeth Dehner joins the Enterprise to study how the crew responds to emergencies in deep space. When the ship crosses the barrier at the edge of the galaxy, she and Gary Mitchell are both affected, though her powers develop more slowly.
Initially sympathetic to Mitchell and doubtful of Kirk's fears, she follows him after he escapes on Delta Vega. Seeing his growing cruelty, she uses her own power to weaken him, allowing Kirk to defeat him, and she dies from the effort. She was played by Sally Kellerman.