Fresh out of Starfleet, the young and impressionable Chekov guides the Enterprise and heads security while also supplementing other areas onboard.
As helmsman, Sulu pilots the U.S.S. Enterprise during its five-year mission. As third officer, Sulu often takes command in the absence of superior officers.
James T. Kirk
Arguably Starfleet's best commanding officer, Captain Kirk is the sense of authority in the Enterprise's initial five-year mission to boldly go where no man has gone before.
Embracing his half-Vulcan side, Spock applies logical and reason to solving problems encountered by the Enterprise.