The Star Trek franchise is famous for its captains, but now it's time to shine some light on the second-in-command, a role that appears in almost every Star Trek series. Also known as Number One or the XO, this character in Star Trek doesn't always get as much attention as the captain or other certain characters, but they're often just as important. Some of the most interesting and endearing characters had the role or authority of a second-in-command, even if they didn't officially carry the title.After 50 years of Trek, the franchise has seen a number of Starfleet's best officers stand on the bridge to back up their equally famous captains. With the stories of Star Trek as popular as always, there will always be new names to add to this list that have boldly gone where no one has gone before.
7 T'Pol — Enterprise
T'Pol appears in the relatively recent series Enterprise, but chronologically she was one of the first non-humans to serve as an officer in Starfleet at all, let alone as a second-in-command. This series takes place during a time before Vulcans were allied with humans, and other members of the Enterprise crew thought of her as a spy and an outsider.
T'Pol was assigned to the Enterprise to guide the ship in exchange for access to the human's star charts and information about the Klingons. She's had a few opportunities to take command while Captain Archer was indisposed or incapacitated.
6 Saru — Discovery
Saru holds a number of distinguished titles in Starfleet. The Kelpians are a race that was introduced recently with the release of Star Trek: Discovery, and he was the first Kelpian to leave the homeworld of his own free will. He was also the first of his kind to serve in Starfleet and had roles on two Federation ships, the Shenzou and the Discovery.
While serving on the Shenzou, Saru was a science officer. It wasn't until Lorca assumed the position of Captain of Discovery that Saru was promoted to the role of his second-in-command, and he took over at several points when Captain Lorca was unavailable. Despite his cool, even shy demeanor, Saru distinguishes himself as one of the most knowledgeable, inspirational, and courageous members of the crew, more than worthy of the first officer's chair.
5 Kira Nerys — Deep Space 9
Kira's official title was Commanding Officer, but if it was a question of authority, only one person outranked her on Deep Space 9, and that would be Commander Sisko. Her gritty past as part of an underground military operation was perfect given the tone of the show, which marked an era of dark, experimental television that was more dystopian than before.
When Kira is first introduced, she's a dedicated member of the Bajoran military and a member of the Cardassian Rebellion, and she doesn't have a lot of love for Starfleet. However, she eventually comes to realize that the Federation can help ensure the safety of Bajor and becomes Sisko's second-in-command.
4 Chakotay — Voyager
Chakotay has an interesting backstory before he joined the crew of Voyager as its first officer. He was formerly the Captain of the Val Jean, a Maquis Resistance ship, so his credentials as a leader are more than intact. He also seems to have some background as a tough guerrilla fighter, a handy skill in the wilderness of uncharted space.
Janeway made Chakotay her second-in-command partly because of his resume, but also due to his status with the Maquis Resistance. Both captains knew that their crews had to work together to survive and get back to Earth, despite their competing ideologies. Janeway making Chakotay her second-in-command was as symbolic as it was practical.
3 Tuvok — Voyager
Tuvok was serving as a double agent on Chakotay's ship, which is part of what led to their capture by Voyager, so he was the target of some resentment on the part of the crew he had betrayed. Making him the second-in-command would have been too awkward politically, with Janeway intending to lead both crews.
Given the extraordinary situation in which Voyager found herself, Janeway had to make sure that all of her options were open and didn't want Tuvok to stop being a spy. Although Chakotay might have been the one with the official title, Janeway turned to Tuvok just as often, perhaps even more, when it came to questions of planning and authority.
2 Una Chin-Riley — The Original Series
The very first second-in-command to appear in the Star Trek franchise was also one of the best. The pilot episode of the original series had a few key differences where the crew was concerned, with Christopher Pike as the Captain and Una Chin-Riley as his Number One.
Most viewers will recognize Una as Pike's second-in-command in "The Cage," and her childhood and education are described in the novel "Vulcan's Glory." She was played by Majel Barrett in the original show, the same actor who played Nurse Chapel in later episodes. The role has been reprised by Rebecca Romjin in Discovery, and the actress will return to the role in the upcoming Strange New Worlds.
1 Spock — The Original Series
The character of Spock has appeared in most of the Star Trek films, including those that took place on the Kelvin Timeline. New Star Trek spinoffs often either reference Spock or include him as a character depending on their place in the universe.
After the pilot episode, Science Officer Spock was promoted to second-in-command on the starship Enterprise. Since then, he has been one of Starfleet's most famous and valuable commanding officers, never mind one of the most popular characters on any television show anywhere. The perfect balance to Captain Kirk, he's an icon of Star Trek, and pioneered the franchise's archetype for the Number One role.