Instead of having a primary character and then a secondary/backup characters, you have a stable of characters.
Each player can have multiple characters in the game but only one can be active at a time. The rest are waiting at a home base, etc.
Waiting characters are in the game world but do not earn XP.
Waiting characters can be dismissed from the stable at any time.
There are two ways to create secondary characters:
Any loyal retainer hired (leveled or 0-level) can be promoted to your character stable. This will have the effect of:
In the event of the death or loss of the primary character, one of their retainers is automatically promoted. This allows the player to get right into the action again.
If the player does not have a retainer, then some 0-level NPC or rando around the next corner would be promoted. Other player's retainers cannot be promoted
You can swap the active character for any waiting character you're using any time you're in a safe haven (e.g. town) where the waiting character is located.