Character Description: Onigumo
Onigumo is the immoral man who eventually becomes Naraku. Onigumo's past is a mystery, but it appeared he was a bandit who had been inflicted by severe burn wounds, making him too weak to move. He was cared for by Kaede and Kikyo. As time went on, he began to develop feelings for Kikyo to his disgust. But then he learned that she was in love with InuYasha.
So Onigumo let demons eat his body to give his soul a new vessel in return, so he could have Kikyo as his wife. When a fire started in Onigumo's cave, it was thought that he had died, consumed by flames. But there was a spot in the cave where no moss or grass would grow....the spot that Onigumo once lay and Naraku was born.
However, much to Onigumo's horror, as the newly born Naraku's desire was to kill Kikyo, overwhelming him as he struck Kikyo down. Once Kikyo's funeral pyre was done, Naraku 'banished' Onigumo deep within his subconscious in state of deep-sleep. But despite it all, Onigumo's human soul made Naraku a half-demon with Onigumo's feelings for Kikyo, which is symbolized by spider mark on his back. It is due to this that Naraku wants the Shikon Jewel to make himself a true demon, and purge himself of Onigumo's influence.
Naraku succeed in purging "Onigumo" from his body, in the form of a faceless man. The faceless creature killed many men for their faces, until a young priest named Muso crossed his path. Onigumo killed the priest and took not only his "beautiful face", but his name as well. However, Onigumo has no recollection of his past and though a mass-murder spree could help him remember. But when he encountered Kagome, and ended up at the cave where he once was near death, he regained his entire memory.
The now demon Onigumo was a powerful foe, able to regenate and reshape his body. However, Naraku realized that he was not strong enough to survive without Onigumo's heart, and thus reabsorbed him. But by the time Naraku succeeded in removing Onigumo completely, splintering Onigumo's being into new enties: Akago (Onigumo's immoral nature) and the various small, white, deformed child-like creatures that dwell inside Mt. Hakurei and eventually melded into a spider-like creature in the form of Naraku's head (Onigumo's feelings for Kikyo). However, Onigumo was reasorbed back Naraku after he came to the conclusion that Onigumo's perversion is needed to corrupt and can easily be purified if Kikyo should find him. However, as he died fighting InuYasha and company, Naraku realized that Onigumo's desire was truly his own after learning that Shikon Jewel didn't make him a full demon as he intended it to be.
I'm told Onigumo's name means "Orge Spider" in Japanese.