Lex (Trill host)

Lex Gotens (more commonly referred to as just Lex) was the girlfriend to James Gotens, and was the subject of a self-depreciating Trill symbiont exchange. 

Lex Seifer
Sometime between 2375 and 2377, Lex met James Gotens, who had convinced her to exchange her own Seifer (symbiont) with the opposite universe counterpart of his own symbiont. The notion was that they would become closer in this way.

When she agreed, both James and Lex pretended to be Trill technicians who were scheduled to do work on the advanced shuttle USS Paroga aboard the USS Phoenix-X.

Using a specifically created holographic program aboard the Phoenix-X, the two captured Commander Gotens and operated on both he and Lex. The result was an exchanging of symbionts. ("Secret Shuttles, Part II")

Lex Gotens
After the operation, Lex and James escaped into the mirror universe, using an iso-star. The now Commander Night Seifer gave chase, but was unsuccessful.

Lex continued to be at James' right side for most of his scheming and was part of his crew when he acquired his own starship. In 2382, she took part in going back into the primary universe and hijacking the USS Phoenix-X for the Klingon-Cardassian Alliance. Unfortunately, their plans were thwarted by the crew and the sentience of her previous symbiont, and she was handed over, as a prisoner, to the Terran Rebellion. ("Mirrorlyness!")