The owner of a building or a ship is the first character shown inside. This will be the first character to have entered the building or ship, unless another character attacked the previous owner and taken position at the head of the list.
For example, assume the following characters are on a ship, the HMS Pinafore :
Candide the Captain , with ten sailors Osswid , accompanied by: Feasel the Wicked 
Since Candide is first in the ship's character list, he is the owner of the ship. Only Candide may issue sail orders, or change the ship's name. If Candide were to leave, Osswid would become the new captain of the ship.
The owner of a building or ship may determine who may enter with the
admit order. The default is to refuse entry to units from other
If the first character inside a building leaves, he is no longer the owner.
A building is a castle, tower, inn, temple or mine.