An Acamarian clan all but exterminated by the rival Lornak, whose last five survivors altered one of their number, Yuta, into a slowly ageing carrier of a clan-specific virus.
Clan Tralesta was one of the feuding clans of Acamar III. About eighty years before 2366 it was destroyed in a Lornak raid, and only five of its members escaped.
The survivors chose the youngest, Yuta, to carry their revenge. Her cells were changed so that she aged very slowly and her body carried a microvirus harmless to everyone except those of Lornak blood. She spent the following decades finding and killing them one at a time.
In The Vengeance Factor, Yuta travels on the Enterprise as cook and taster to the Acamarian sovereign Marouk. The crew link her to the death of a Lornak half a century earlier, and Riker is forced to vaporise her when she will not turn away from the Gatherer leader Chorgan, the last of her targets.