He was also working in engineering when a group of renegade Ferengi took over the ship. He was then among the Starfleet officers who were brought into one of the transporter rooms and beamed off the ship. (TNG: "Rascals")
He later switched to security and at some point was responsible for setting up the duty roster for the security department. When he presented it to security chiefWorf, who was curious about the whereabouts of his father at this time, Worf bluntly refused to accept the roster, ordering Lopez to do it again with the assignments ordered by priority and to finish it by 0900 hours. (TNG: "Birthright, Part I")
Ensign Lopez was played by recurring background actor Tony Cruz, who received no credit for his appearances.
He was identified by name in "Birthright, Part I".