Y'Sek was a Hazari man working as a bounty hunter in the Delta Quadrant in the 24th century.
In 2375, Kurros of the Think Tank hired Y'Sek and his partners (while disguised as a Malon) to obtain Seven of Nine and bring her to them. Upon the first encounter of the USS Voyager and the Hazari, Y'Sek demanded their surrender and would not give up the name of who hired the Hazari, even when offered a larger payment from Kathryn Janeway. During a second attack, Y'Sek was captured and learned that he had been tricked by Kurros. He agreed to help the Voyager crew get back at the Think Tank, as other races would pay big bounties for them, and attacked their vessel when it was forced out of subspace. (VOY episode: "Think Tank")
External link[]
Y'Sek article at Memory Alpha, the wiki for canon Star Trek.