A planet purchased and inhabited by the immortal Flint, where Kirk seeks the drug that can cure an epidemic aboard the Enterprise.
Holberg 917G is a planet in the Omega system where the immortal Flint lives in seclusion with his ward Rayna Kapec and a robot servant. He bought the planet decades earlier and keeps an impressive collection of masterpieces and books.
In Requiem for Methuselah, the Enterprise crew is suffering from Rigelian fever, and Kirk comes to the planet in search of ryetalyn, the only cure. Flint lets them stay, and Kirk falls for Rayna, who turns out to be an android.