The Ennis were a faction of an alien race in the Gamma Quadrant. They were led by Golin Shel-la.

Several hundred years ago, the Ennis began a long-running war with the Nol-Ennis on the planet Tevlin-De. The cause of the war was soon forgotten, some believing it to be over land or water. As a punishment for not being able to end the fighting and as a deterrent for the other factions on the planet, the Ennis and Nol-Ennis were exiled to a moon. As an additional punishment, Tevlin-De's leaders created nanite-like bio-mechanical microbes that resurrected people after death, forcing the Ennis and the Nol-Ennis into an eternal war. (DS9 episode: "Battle Lines", DS9 novel: Rising Son)

In 2369, Benjamin Sisko and Opaka Sulan were able to mediate a short cease fire between the two groups. (DS9 episode: "Battle Lines")

Over several years, Opaka served as a negotiator between the Ennis and the Nol Ennis. In 2372, she mediated a cease fire that lasted several days. Although it did not endure, it marked the end of the fighting. The two factions were later united, becoming known as the Sen Ennis. (DS9 novel: Rising Son)