GoyCho

Lieutenant GoyCho was the armory officer aboard the USS Phoenix-X in the late 24th century. He was also able to double in Engineering when necessary, and was known to work in the Security department at times. 

J3 torpedoes
GoyCho was the sole technician for the J3 torpedo technology aboard the Phoenix-X, spending years working on every aspect of them - from deciphering its Dominion origins to finding a way to apply it to Starfleet technology. His time spent on the project was sparring, depending on whether he would be preoccupied with a more important mission or not. GoyCho's progress was monitored closely by Section 31.

In 2382, he had finally completed several modifications to the torpedo design. Section 31 then arranged a test between the Phoenix-X and the Tal Shiar vessel, Caterina. Unfortunately, a virus created by both Amp's and Omega's programs had infected the torpedo, thus putting an end to its development. ("Experimentalism", "The 47's")

Personal information
GoyCho, along with Ensign Dan, was an avid lover of a food called yak cheese. ("The Links' Traitor")

He also has been known to "sleep around". In 2375, he had coupled with Ensign Jineen, while she was seeing Commander Gotens. But at the same time, GoyCho was dating someone else on the crew. ("Retrieval")
 * GoyCho was written as a Bolian in this episode.

Mirror Universe double
GoyCho's mirror universe double is a Nausicaan. When Captain Daniel needed a guard to beat the Doctor, GoyCho was called in to do the deed. GoyCho was killed along with the rest of the crew when the mirror Phoenix-X was destroyed in 2375. ("Pure Evil")
 * It is possible GoyCho was the mirror Daniel's personal guard, or lackey.

The mirror GoyCho would be brought back to life, in 2383, with the rest of the crew by Rein, an omnipotent being testing out his powers. Since the crew of the Phoenix-X included Klingon-Cardassian Alliance sympathizers who eventually enslaved the human portion of the crew - it is possible that the mirror GoyCho, being a non-human, was part of these sympathizers. ("Broken Pieces")

Background information

 * GoyCho was an on-the-fly created characters that remained throughout the series. In several episodes he was a difference species: in "Pure Evil", his mirror character was written as a Nausicaan, and in "Retrieval", he was written as an overweight Bolian.