Arbiter
'ARBITER, noun [Latin]
1. A person appointed, or chosen by parties in controversy, to decide their differences. This is its sense in the civil law. In modern usage, arbitrator is the technical word.
2. In a general sense, now most common, a person who has the power of judging and determining, without control; one whose power of deciding and governing is not limited.
3. One that commands the destiny, or holds the empire of a nation or state.