Kabaka Buganda was a human trader who owned the non-aligned space station Orillius 1. He was romantically involved with Nyota Uhura, but their relationship ended in 2265 when their career paths took them in different directions.
Buganda resurfaced in Uhura's life when the crew of the USS Excelsior intercepted a pair of smugglers taking dilithium crystals to the Orillius 1 station. Uhura, along with Hikaru Sulu and William Bearclaw, visited the station posing as ex-Starfleet personnel hoping to become traders. Buganda was quite happy at the prospect of another chance with Uhura—a happiness Uhura seemed to share until she discovered he was involved in slave trafficking.
Uhura and her crewmates soon escaped only to be pursued by Buganda and his operatives. Though Buganda was able to destroy the Starfleet officers' vessel, Uhura and her crewmates transported to the lower decks of his ship that housed a number of slaves. The slave were immediately set free and revolted against their former masters with the help of Sulu, Uhura, and Bearclaw. Unprepared for such an action, Buganda and his operative were captured in short order.
Before being detained aboard the Excelsior, Buganda was still puzzled at his former lover's betrayal. Uhura explained that her responsibilities to the Federation, to herself, and to life, had to be met. (TOS comic: "The D'Artagnan Three")
Kabaka is the title carried by the king of the Kingdom of Buganda, a kingdom of 52 clans within the present-day nation of Uganda.