Characters make up the people in a game. The two most commonly used categories of characters are Player Characters (PCs) and Non-player characters (NPCs). Player Characters are controlled by the Players, and the story usually follows them. Non Player Characters are controlled by the GM and make up all of the world, except the PCs.
Full, or nearly full, write ups of fictional characters are under Category:Characters. Write ups of historical characters are under Category:Historical Characters. A form to write up full characters can be found at Character Layout Form. NPCs are generally handled through the {{GURPSNPCTraits}} template with beasts and monsters handled via {{GURPSCreature}}