In 2267, the USS Enterprise discovered the Shore Leave Planet, an artificial world where complex machinery could bring fantasies to life. After he picked up a flower, Kirk, now a captain, thought of his long-lost love. Reading his thoughts, the planet computer created a robot that was a duplicate of Ruth. (TOS: "Shore Leave")
Ruth, or rather, her facsimile was played by Shirley Bonne.
The character was not, however, cast as she was described in the final draft of the script, which defined her as "A truly beautiful girl with long black hair. Her whole aspect is gentle, warm, welcoming."
Lines spoken by Ruth that were ultimately cut from the final draft of the script clarified what had happened between the two, stating, "You thought you'd lost me, didn't you – after graduation, after your first star cruise...?"