In J.R.R. Tolkien’s legendarium, the ring forged by Sauron to control the other Rings of Power is the One Ring.
Sauron secretly forged the One Ring in the fires of Mount Doom during the Second Age. He placed a large portion of his own power into it, giving him influence over the other Rings of Power and making the ring central to his attempt to dominate Middle-earth. Its inscription is written in the Black Speech of Mordor.
The One Ring can make its wearer invisible to ordinary observers, but invisibility is only a side effect of its deeper power. It also exerts a corrupting influence and seeks to return to Sauron. The ring can be destroyed only in the fire where it was made, which is why Frodo’s quest ends at Mount Doom.
The Three Elven Rings were not directly controlled in the same way because Sauron did not touch their making. The One Ring is therefore not simply another magical ring; it is the instrument of Sauron’s power.