Ungoliant was a huge, spider like creature that lived in the land known as Avathar, an uninhabited area of Valinor that lay between the southern ocean and the Pelóri Mountains. She possessed the power to weave a web of darkness known as unlight.

Ungoliant made an alliance with Melkor, and when he attacked the Elves and the Valar, Ungoliant destroyed the Two Trees and drank their sap.

Ungoliant assisted Melkor in killing Finwë, and in the theft of the Silmarils. She then accompanied him in his flight across the Helcaraxë to Middle-earth. Once in Middle-earth, Ungoliant and Melkor fell to disagreement over the Silmarils. Ungoliant was so powerful that Melkor himself had to call upon his legion of Balrogs to assist in driving her off.

Ungoliant fled to the Valley of Death in the Mountains of Terror in Beleriand. There, she bred with the spiders to create a race of monstrous spiders. Shelob, the great spider who was the watcher of Cirith Ungol during the War of the Ring, was among Ungoliant's offspring.

Ungoliant wandered south after the sinking of Beleriand into the deserts of Harad where it is probably that she consumed herself from starvation.