First officer

First officer was an title used by Gallifreyan soldiers and, in a parallel universe, the United Federation of Planets.

Once, the Ten killed a squad of Gallifreyan soldiers on Dalgar by hypnotising the first officer to kill the commander, then the second officer to the first officer, and so on. The Ten let Tessno survive the incident so that she could tell Gallifrey about what he had done. (AUDIO: Stop the Clock)

In the 23rd century, Mr Spock was the first officer of the USS Enterprise, a vessel of the Federation Starfleet. (COMIC: Assimilation²)