Sauron was the primary antagonist in the Lord of the Rings series but why was the character a disembodied eye throughout the franchise? Sauron had a long and dark history in J.R.R. Tolkien's vision of Middle-earth. The Dark Lord's fall and physical manifestation was a focus of the trilogy of films directed by Peter Jackson.
Sauron was around long before the First Age where he was said to be a Maia, a spirit that descended to create the world. During that time, he went by the name Mairon, but he later became focused on world domination. He was then referred to as Sauron, which meant "the abominable". Sauron then became the Lieutenant of Morgoth and served his new master in the conflicts in Middle-earth. After a series of wars and battles, Sauron was sent into hiding for hundreds of years.
Sauron reappeared during the Second Age and gathered power in the Mordor. He began accumulating an army of Orcs and Trolls, while he also manipulated weak-willed men who were driven by wealth. Sauron wanted powerful Elves on his side so he forged the Rings of Power. He gave the rings to various Elves, Dwarves, and Men as he referred to himself as the "Lord of Gifts". Along with the Rings of Power, he secretly forged the One Ring, the ring that could rule all the others and dominate Middle-earth. When Sauron was defeated by Prince Isildur of Gondor, his finger was severed, as was the Ring. He also lost his physical form and from then on, Sauron manifested as an Eye.
Sauron's forging of the Rings was featured at the beginning of 2001's The Fellowship of the Ring. His physical form was shown as a figure in black armor that stood nine-foot tall. This description was also used for various flashbacks of Sauron's previous life throughout the trilogy. After losing the One Ring, Sauron's physical body was destroyed as his power stemmed from the ring. He was thought to have vanished from Middle-earth but his essence still existed. During the Third Age, Sauron returned as a giant flaming eye that sat on top of Barad-dûr, Mordor's stronghold.
The all-seeing Eye still had control of Middle-earth as he oversaw all of the ongoings within the realm. He then spawned an army of Orcs and enslaved men to carry out his war to win back the One Ring. The Eye of Sauron, which is what he was commonly referred to, became a symbol of fear and power for those involved in the War of the Ring. When Sauron caught wind of Frodo Baggins and the One Ring's journey, he set a target on the hobbits from the Shire.
Sauron made an ally in Saruman the White, in an effort to bring his wrath upon Middle-earth. Despite his mission, Sauron still had his sights set on reacquiring the Ring. By Return of the King, Gandalf and Aragorn had one more chance at defeating Sauron. They successfully drew out Sauron's army to empty out the forces in Mordor. This allowed Frodo and Sam to travel to Mount Doom. After a scuffle with Gollum, Frodo managed to throw the One Ring into the volcano, destroying Sauron's life force and putting an end to the major mission in Lord of the Rings. Barad-dûr crumbled and the Eye, Sauron's last remaining form, turn into a dark cloud and blew away.