From Tolkien Gateway

Underking was a special appointed office of the Rohirrim in which the officer was entitled to act as if he were the king. In wartime, if the King of Rohan was absent from home while commanding an army, the Underking ruled in his place. Alternatively, the office holder served as the field commander of the army if the King remained at home. However, in war an old King was not supposed to send his Heir to battle beyond the realm unless he had at least one other son. During peace an Underking could be appointed only when a sick or aged King deputed his authority, and the holder of the position was then considered the Heir to the throne.[1]

See also[edit]


Ranks of the Rohirrim
First Marshal of the Riddermark · Second Marshal of the Riddermark · Third Marshal of the Riddermark · Marshal of the East-mark · Marshal of the West-mark · Underking