In the game, there should definitely be either a main single entity, or perhaps a league of evil villains who your character should encounter at various points throughout the game. Whether they are set specific points, or rather, generated ones. Maybe if there was a league of villains, there could be a specific "Type" or something that each enemy is. Example: On an arctic-based planet, the enemy of the league could be some form of magically gifted ice wizard. Just a suggestion.