Zlangco was an alien male and the leader of the Nol-Ennis for several hundred years.
Zlangco and his group, as well as Golin Shel-la's Ennis faction, were exiled to a moon in the Gamma Quadrant by his homeworld Tevlin-De's leaders for not finding a way to stop their long-running war. As an additional punishment, Tevlin-De's leaders created nanite-like bio-mechanical microbes that resurrected people after death, forcing the Nol-Ennis and the Ennis into an eternal war. Shel-la and his people died countless times over decades and were always resurrected and healed of their injuries. (DS9 episode: "Battle Lines", DS9 novel: Rising Son)
In 2369, Benjamin Sisko managed to Zlangco and Shel-la to meet after Julian Bashir began investigating a way to deactivate the artificial microbes. Zlangco was suspicious and believed it part of an Ennis plan to kill more members of his faction. The cease fire lasted only hours before the two groups began killing each other again. (DS9 episode: "Battle Lines")
Over the next several years, Opaka served as a negotiator between Zlangco and Shel-la . In 2372, she mediated a cease fire that lasted several days. Although it did not last, it marked the end of the fighting. The two factions were later united, becoming known as the Sen Ennis.
In 2373, Zlangco witnessed the Ascendant Raiq's ship crash on the planet. Zlangco and the others were later able to leave the moon, as Raiq destroyed the satellite network, disabling the artificial microbes.
By 2376, Zlangco, Opaka and several other members of the Sen Ennis were living on Ee. After Opaka encountered Jake Sisko. she decided it was time to return home and said goodbye to Zlangco and the others. (DS9 novel: Rising Son)