Frank da Vinci was a background performer and Leonard Nimoy's stand-in on The Original Series, seen in dozens of episodes as Lieutenant Brent, the security guard Vinci and other crewmen.
Frank da Vinci worked on The Original Series from its first season to its last, primarily as the lighting stand-in for Leonard Nimoy. Like the other regular stand-ins he was also put into uniform, and he can be spotted in the corridors, on the bridge and in landing parties in a large share of the episodes.
His best-known identity is Lieutenant Brent, a crewman usually posted at a bridge station in the first season, including The Naked Time. In later episodes he generally wore a red shirt as a security guard, and the character was occasionally addressed by the performer's own surname, Vinci.
He rarely had dialogue, but his long service makes him one of the most often seen members of the Enterprise crew after the credited cast.