The One Ring answers to Sauron alone. It has no other master.
6 seconds sound clip from the The Lord of the Rings: The Fellowship of the Ring movie soundboard.
You can hear this line at 01:40:08 in the Blu-ray version of the movie.
Quote context
[...]
- It is a gift. A gift to the foes of Mordor. Why not use this Ring?
- Long has my father, the Steward of Gondor, kept the forces of Mordor at bay.
- By the blood of our people are your lands kept safe.
- Give Gondor the weapon of the enemy. Let us use it against him.
- You cannot wield it. None of us can.
- The One Ring answers to Sauron alone. It has no other master.
- And what would a Ranger know of this matter?
- This is no mere Ranger. He is Aragorn, son of Arathorn.
- You owe him your allegiance.
- Aragorn. This is Isildur's heir?
- And heir to the throne of Gondor.
(IN ELVISH) Sit down, Legolas.
[...]