Just as in traditional RPGs, each player assumes the role of one Player Character (PC). Unlike most traditional RPGs, FK tends to be rather deadly and involve many characters on the player side.
Note: To avoid confusion, the term "party" is used informally only and never as a rules term. When it does occur, it means all the PCs and Followers currently together.
In addition to his PC, each player is expected to indirectly control various supporting characters, called Followers. Each player controls his Followers in combat and most role-playing situations, and can share this control freely with other players or the GM whenever it's convenient or improves the game. However, the GM may override Follower decisions and take control of them whenever necessary, for example when loyalty or discipline are in doubt, or in order to pursue a Follower's particular motives.
A group of up to 6 characters under a common Leader (typically a PC) is called a Squad. Multiple Squads make up a Company, and multiple Companies can sometimes form an Army. PCs will usually share one Company, with each of them directly controlling a Squad, but other constellations are always possible.
Squads, Companies, and Armies usually have a Leader, conferring various advantages on the group. To represent this organically, Squads should be designed around natural authority figures. Examples include hirelings responding to a captain, a bunch of siblings to the eldest, a mob to a charismatic instigator, etc.
While there may be social reasons to follow a less experienced Leader, mechanically a Follower cannot benefit from a Leader who isn't at least 1 Level higher than him. When a benefit applies to the whole group, the Leader must be higher Level than at least half of its members. The same applies for Companies and Armies, except it affects the Leaders of their subordinate groups instead of Squad members.