Grima Wormtongue

Gríma Wormtongue was the chief advisor to King Théoden of Rohan before being exposed as an agent and spy of Saruman. He ends up being the killer of Saruman. 
== Biography ==
Little is known of Gríma before he became counselor of Théoden in Edoras. His childhood is a mystery. What is known is that Gríma, son of Gálmód, and a native of Rohan, joined the service of Saruman in secret and worked as a spy to weaken Théoden and his kingdom, weakening the king's mind and body with false counsel and poisons.
Gríma was captured by the Nazgûl in the fields of Rohan, while on his way to Isengard to inform Saruman of Gandalf's arrival at Edoras. He was interrogated and divulged what he knew of Saruman's plans to the Nazgûl, specifically his interest in the Shire and its location. Previously, the location of the Shire had been unknown to the Nazgûl, but they knew it to be the home of "Baggins," whom they thought still had the Ring. Gríma was set free, but only because the Lord of the Nazgûl saw that he would not dare tell anyone of their meeting and might do harm to Saruman in the future. The Nazgûl set out immediately for the Shire. Had the Ringwraiths not captured Gríma, they would instead have pursued Gandalf into Rohan, and possibly not have found the Shire until much later, giving the Hobbits and then the Fellowship a considerable head start.
It is likely that Saruman had promised him Éowyn, the king's niece, as a reward for his services; Wormtongue is accused of "watching her under his lids and haunting her steps." It is also possible that he had Dunlending ancestry, since he was darker-haired and physically smaller than the other Rohirrim.
Gríma banishes Éomer entirely from Rohan. When Gandalf frees Théoden, the king nearly kills Gríma until Aragorn intervenes. Gríma then spits on Aragorn's hand and flees, arriving in Isengard to give Saruman vital intelligence of Théoden's movements.
After Gandalf ended Gríma's control of Théoden and releases the King, "many things which men had missed" were found locked in his trunk, including Herugrim, the blade of Théoden. he is depicted as dark-haired, emaciated and eyebrowless, wearing black robes with dark fur, as well as being extremely pale and gaunt. 
After Gandalf ended Gríma's control of Théoden and releases the King, "many things which men had missed" were found locked in his trunk, including Herugrim, the blade of Théoden. With his betrayal revealed, Théoden presented Gríma with a choice: either ride into battle for the King or be exiled. Choosing the latter, he went to dwell with Saruman at Orthanc.