Crewmates are your characters in-game. They allow you to take actions, specialize in the various roles you can play, and interact with Influence. You do not control these Crewmates in first or third person, but each action you take is completed as if you are doing it with all of your various active Crewmates as a single unit (a "crew").
A crew is required to play Influence and is made up of at least one, and a maximum of five, active individual Crewmates, one of which must be selected as the Captain.
Each player can have as many Crewmates as they want, but are limited to having five active at any given time.
When inspecting your profile other players will be able to see your various crewmates that make up your crew, their stats, their bonuses, and of course their unique outfit and looks.
There are a couple different paths to creating crewmates.