Sergio Mendoza was a 23rd century Human male. By the late 2270s, Mendoza was serving in Starfleet as a security guard aboard the USS Enterprise. Mendoza accompanied Commander Spock, Dr. Weinstein, Commander Montgomery Scott, and two other security people, Sergeant Jerry Workman and Bobbi Wagner, on a landing party to Abigail, one of the three moons of the planet Cathy in the Novak system. They crossed a prairie and found one-third of the lost treasure of Vulcan. Mendoza often had occasion to warn Wagner to be more suspicious of the alien environments in which they found themselves. (TOS novella: The Vulcan Treasure)