Sauron, the primary antagonist in J.R.R. Tolkien’s Middle-earth legendarium, meets his end in the climactic moments of The Return of the King. It is not a single character who directly slays Sauron, but rather a series of events leading to his fall.
When the One Ring is finally destroyed by Frodo Baggins in the fires of Mount Doom, Sauron’s power is shattered. His physical form was already weakened as he relied heavily on the Ring for his strength and influence. With the Ring’s destruction, Sauron is ultimately defeated and his spirit is rendered powerless. In this way, Frodo, along with the Fellowship and their combined courage, is responsible for Sauron’s demise.
It is important to note that while Frodo does not strike Sauron down in a traditional sense, the act of destroying the Ring is what leads to Sauron’s ultimate downfall. His reign of terror comes to an end as the Dark Lord’s spirit fades away, leaving Middle-earth free from his menace.