Doctor Seth Mendoza, was the Federation representative during the negotiations for the Barzan wormhole aboard the USS Enterprise-D in 2366.
Mendoza was a skilled and respected negotiator, particularly by Devinoni Ral who represented the Chrysalians at the proceedings. However, it was DaiMon Goss who saw Mendoza as the greatest threat to the Ferengi bid for the wormhole and so he allowed Doctor Arridor to use distilled pyrocytes to provoke an allergic reaction in Mendoza. Mendoza fell ill and had to be replaced in the negotiations by Commander William Riker.
Riker was reluctant to take on the role, despite having been previously praised by Mendoza as an astute observer and a good poker player. (TNG: "The Price")
Mendoza was played by actor Castulo Guerra; his first name was not mentioned in the episode but is from the shooting script.