Bialbi

Bialbi was a non-corporeal lifeform identifying as the High Mentalic of the planet Hrakkour IV. When the Klingons under the Kenka family colonized the planet around the 22nd century, Bialbi remained hidden to their archeological digs. However he waited in silence.

When Vlict Kenka judged the being Quetzecoatl, he sent James T. Kirk and his landing party in the dungeons and tunnels below the surface. Then Bialbi chose to reveal itself to Kirk when he activated the green Light of Knowledge.

Bialbi stopped the Klingons from executing Quetzalcoatl, and judged Kenka to be guilty of genocide. Bialbi sentenced Kenka to death as the penalty to unjustice, however Captain Kirk intervened on Kenka's behalf, and Bialbi relented.

Bialbi ordered Kenka to leave the Hrakkour system and never return on pain of death. Bialbi further ordered that no Klingon vessel was to ever return to Hrakkour, however he invited Captain Kirk to return, finding his level of social development pleasing. 
 * There are several outcomes to Kenka's fate. Kirk can withdraw from the trial and leave Quetzecoatl on his own in which case Kenka presumably executes him unobstructed. If Kirk brings Kenka to be tried by the Bialbi, he can choose to leave him to be executed.