An android of great intellect built by the immortal Flint, whose awakening emotions for Kirk ultimately destroyed her.
Rayna Kapec appears to be Flint's young ward on Holberg 917G, a brilliant woman educated in many fields of knowledge. In reality she is an android, the latest of several that Flint built in the hope of creating a companion who could share his endless life.
Flint deliberately brings Kirk and Rayna together so that she will develop human feelings. She falls in love with Kirk, but when she is forced to choose between him and Flint, the conflicting emotions overload her and she dies. Kirk is left so grief-stricken that Spock later uses a mind meld to help him forget her.