Baroner was a name given to James T. Kirk by Ayelborne during his visit to Organia and subsequent impersonation of an Organian. The guise was necessary to evade the scrutiny of Commander Kor and the Klingon occupation army. The USS Enterprise was forced to flee a superior Klingon force, stranding Kirk, who needed to remain undetected.
Ayelborne later betrayed "Baroner" to the Klingons, when Kor suspected "Baroner", and it looked likely that Kirk would be subjected to the mind scanner. Inasmuch as the mind sifter would have pierced the ruse as well, it is unclear how much harm Ayelborne's revelation did – but it was one more event that built up a reservoir of disgust for the kind of people Kirk then believed the Organians to be. (TOS: "Errand of Mercy")