Foreign leaders are Sims who govern the various territories of the world outside of the kingdom in The Sims Medieval. Every territory has its own leader with their own unique title (e.g. "Snoozemeister" Bob or "High Priestess" Alice), who will permanently reside in the castle after an alliance is formed between that territory and the Kingdom. Should the Kingdom annex another territory, whether through violent or peaceful means, its current leader will remain in power but will no longer have sovereign authority. If a foreign leader dies, a new Sim will claim the position.
Leaders are, otherwise, similar to other Sims. They can be dueled/sparred with or even sent to the Pit of Judgement. A good relationship with these Sims will not affect the loyalty of the territories they command, although if befriended they will never decline to say what edict they are planning on voting for. Foreign leaders tend to make good marriage candidates for the monarch, as unlike many other characters they can always be found in or around the castle.