Mendon specifically requested to be assigned to the USS Enterprise-D. He came aboard at Starbase 179 with the rank of ensign. Wesley Crusher, at first, thought Mendon was his friend Mordock, but Mendon pointed out that Crusher was mistaken, remarking that as they were from the same geostructure, they would look alike. (TNG: "Coming of Age", "A Matter Of Honor")
Mendon comported himself in a manner very confident of his own abilities, and after observing the bridge crew, he attempted to suggest some changes to Captain Picard in order to make things "more efficient". After Picard brushed off his approach, referring Mendon to his supervisor Lieutenant Worf, Mendon scanned the Klingon starship IKS Pagh, with which the Enterprise-D was making a rendezvous. He discovered a subatomic bacteria eating away at the hull of the Pagh, but did not report it until a similar lifeform was discovered on the hull of the Enterprise-D. He revealed that he had merely followed Benzite procedure, which required that a problem not be reported until a solution had been found. When Picard informed Mendon that he should have followed Starfleet procedure, not Benzite procedure, and alerted his superiors to the problem immediately, he became despondent. He told Wesley Crusher that he thought he had failed, but Crusher consoled him, telling him he should attempt to find a solution to the problem.
Mendon was played by actor John Putch in his second of three Star Trek appearances. Putch previously played the identical-looking Mordock in "Coming of Age", awarding him the honor of being the first Star Trek: The Next Generation guest star to play two separate characters from the same species. (Star Trek: The Next Generation Companion, 3rd ed., p. 75)
Of returning to play Mendon, Putch recalled; "I was all very impressed by that. I thought, 'Ah, they love me, they love me.' What they really loved was that it was me, because they'd spent all that money on making that blue head and it was form fitted to me... I don't fault them for that. I would have done the same thing, but it's funny how you are naive about these things when you're just an actor." 
The makeup department originally created (for Mordock) one major appliance that covered most of actor John Putch's head and additional pieces that covered his upper lip, chin, and eyelids, both of which were an unusual configuration of "puffy eyes" with lids that "folded back on themselves like Venetian blinds." The mouth area and earlobes possessed a set of catfish "feelers" while the overall headpiece was painted blue with oranges and yellows worked in to make the skin color look more lifelike. (Star Trek: Aliens & Artifacts, p. 110)
The script for "A Matter Of Honor" describes Mendon as "a large, blue-skinned officer from the planet Benzar. He breathes through a special device at his chest which converts the oxygen level to his use. He is young, alert, quick moving and as the nature of Benzites, he is always ready to please and demonstrate his abilities."