First mate

A first mate is the second-highest ranking officer aboard a civilian starship, the equivalent of a military organization's first officer.

In 2268, was the first mate of the Windjammer under Captain Black Jack Nova. 

In the 2270s, Jack Corrigan was the first mate of the Werewolf under Captain Solomon Kane. 

In the 2370s, Wayne Sheppard was the first mate of the SS under Kasidy Yates.