Linda Hamilton plays Dr. Kay in Stranger Things season 5.
Hamilton joined the cast of the fifth and final season as Dr. Kay, a military researcher and one of the season's new antagonistic figures. The role was kept undisclosed when her casting was first announced, preserving the mystery around how she would enter the story.
Hamilton is best known for playing Sarah Connor in the Terminator films, making her addition a notable reunion with the 1980s genre tradition that Stranger Things frequently celebrates. The Duffer Brothers said Dr. Kay would have a significant impact on Eleven's journey.
Dr. Kay is not Karen Wheeler, who is played by Cara Buono, and she is not Virginia Creel, Henry Creel's mother. She is also separate from Dr. Sam Owens, the government scientist played by Paul Reiser. Those distinctions make Dr. Kay the single correct answer.