The Twins were two bald magicians. They served the Varden as heads of Du Vrangr Gata and by probing the minds of all who entered Farthen Dûr to make certain they were allies. However, they were actually spies for the Broddring Empire. They had no known individual names.
Time with the Varden
The Twins entered into the service of the Varden during the time of Deynor, who hired them to suppress the Varden's need for capable magic users. After Deynor's death, they continued to serve the Varden under the leadership of Ajihad. At some point, they assumed leadership of Du Vrangr Gata and were put in the position to probe the minds of all who entered the Varden's lair in Farthen Dûr.
After Murtagh, Eragon and Saphira arrived in Farthen Dûr, the Twins were placed in charge of probing their minds to make certain they were allies. Eragon agreed to be probed, though the ordeal was painful. During the probing, Saphira blocked out parts of his mind at his request, including Murtagh's heritage. Murtagh refused to have the same done to him and was imprisoned by Ajihad. They had a great dislike of Eragon, though they tried various times to obtain his knowledge of the Ancient Language. Later, the Twins tested Eragon's skill with magic until they demanded an act of magic that would have likely killed him, at which point Arya intervened. The Twins were then assigned to assist Eragon during the Battle under Farthen Dûr, but Eragon lost contact with them and consequently, was forced to face Durza on his own.
Betrayal and death
During the aftermath of the battle, the Twins and Murtagh were captured by a troop of Urgals and were assumed dead. In truth, the Twins were spies for the Broddring Empire, who had betrayed collaborators to the Empire. The kidnapping had been coordinated by them so that they could take Murtagh to Urû'baen, where he was forced to swear allegiance to Galbatorix. They also betrayed Eragon at the Battle under Farthen Dur by luring him away from Saphira and Arya, thus leaving him vulnerable for Durza to defeat and capture. The Twins also revealed to the king that while they were probing Eragon's mind, they found that his mother was Selena, Morzan's Black Hand, which would have been a devastating secret to the Varden.
The Twins were present at the Battle of The Burning Plains, fighting on the side of the Broddring Empire. Their magic skills were superior to those of the other members of the Du Vrangr Gata and they took a heavy toll on the Varden's forces. Roran, however, was able to come upon them by surprise and crushed their skulls with his hammer.
Personality and traits
The Twins were two identical bald men, who often wore purple and gold robes. Their eyes were close-set and they had thin fingers. They were also tall, being of above-average height.
They were cunning and capable of hiding their true allegiance from the Varden. Saphira warned Eragon that they would use anything a person said or any other leverage against said person. There were, understandably, many in the Varden who did not like them because of their spiteful attitude and desire for power. They could be quite cruel and sadistic, shown when one of the Twins they scanned Eragon's mind he deliberately caused the latter pain and used excessive force to search Eragon's memories.
The Twins were also quite greedy, as they sought to learn the words of the Ancient Language that Brom taught Eragon, and even offered Eragon membership in Du Vrangr Gata so that they could learn his vocabulary. The Twins were arrogant in their abilities, as they told Eragon that they were stronger than him and frequently boasted in possible exaggeration in how powerful they were. They held animosity towards Eragon for declining their offer to join Du Vrangr Gata, as they tried to make him fail in the magical proficiency test they assigned for him.
They were implied to be sadistic in Eldest, as they laughed and grinned as they slaughtered members of the Varden.
The Twins considered themselves very powerful magicians, although the true extent and potency of their powers is worthy for debate, because although Ajihad considered them powerful, Saphira found them to be less powerful as demonstrated by her derision for them. They could have been very powerful by the standards of humans, but Arya was easily their superior, performing magic that was beyond them. Also, their Ancient Language vocabulary was quite limited, possibly even more so than Eragon's at the time of his first arrival in Farthen Dûr.
However, the Twins were stated to be "far stronger" than the average magician in Galbatorix's army. Their advantage was their link through which, assuming they possessed the ability, they were connected allowed them to lend each other strength. They were skilled enough in magic to give Eragon difficulty in completing the exercises they assigned him in his magic proficiency test, forcing him to draw on Saphira's strength to prevail.
The Twins were skilled with mental powers as it was their duty to scan the minds of those who entered the Varden to determine whether the visitors are friends or allies. They were also competent in offensive magic, able to unleash blasts of energy that could sever an Urgal's arm and attack with balls of energy that were powerful enough to kill.
It is possible that the Twins shared a mental link. This may be because they're identical, or some other unknown reason. A mental link is hinted when Roran struck the first of the Twins, the other fell to the ground, "convulsing and emitting a wordless scream." This indicates the other Twin was in severe pain or distress and could well have been caused by a mental link (this is similar to the bond between a dragon and a Rider when some Riders or dragons can go mad when their partners are killed.)
Role in the Eragon movie
The Twins were not featured in the film or the video game, though a deleted scene can be seen on the DVD that has the Twins, both played by Ralph Brown, probing Eragon's mind. The probing is done using flashbacks.
- The Twins were double agents that were masquerading as Varden members, but were actually spies for the Empire