Rayna Kapec
Rayna Kapec was an android – actually the latest of several – built by Flint, an immortal who had wandered the Earth in various personae such as Brahms and Leonardo da Vinci, to be a companion for him.

When the  visited Holberg 917G looking for the cure to a plague that had infected the crew, Flint introduced Rayna as his legal ward, explaining that her parents had been his employees but had died in an accident. Captain Kirk and Rayna became attracted to each other, which at first Flint was happy about. He hoped that this would provide the final step in her creation, stirring her emotions. Later, he became jealous of the relationship.

As Flint and Kirk became involved in a fight over Rayna, her new feelings and the choice between Flint and Kirk overwhelmed her. Rayna, unable to handle such intense emotions, short-circuited, collapsed to the floor and ceased functioning. 

Back aboard the Enterprise, after an exhausted Kirk fell asleep at his desk after ruefully reflecting on everything that happened, Dr. Leonard McCoy said to Spock that he wished the captain could forget Rayna. After McCoy left, Spock granted this wish by using a Vulcan mind meld to erase all Kirk's memories of Rayna. ()

Background information 

Rayna was played by actress Louise Sorel.

Although the signs above the androids clearly read RAYNA, the character's name was listed as "Reena" in the closing credits on the DVD prints. Prior VHS and Laserdisc prints spell the name correctly.

According to the , "Rayna Kapec was named for Czechoslovakian writer , who first coined the term "robot" in the classic science-fiction play entitled ."

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Androids