Sauron is the dark lord in J.R.R. Tolkien’s The Lord of the Rings.
Sauron is the principal enemy behind the search for the One Ring. He forged the Ring in the fires of Mount Doom, placing much of his power into it so that he could dominate the other Rings of Power and control their bearers. The quest centers on destroying the Ring before Sauron can reclaim it.
In Tolkien’s larger mythology, Sauron originally served Morgoth, the first Dark Lord. After Morgoth’s defeat, Sauron became the chief enemy of the later ages. He can appear in different forms across the history of Middle-earth, but by the time of The Lord of the Rings he is represented primarily through his will, armies, and watching eye.
Morgoth is therefore a related but distinct figure. He is Sauron’s former master and the greater ancient enemy of Tolkien’s earlier mythology.