Who is the new rider in 'Brisingr'?

Answer 1

There is no new Rider in Brisingr. It will be in book four. Here follows a synopsis of Brisingr: Eragon, Roran, and Saphira are traveling towards Helgrind, the dwelling place of the Ra'zac, where Roran's betrothed, Katrina, is being held prisoner. Eragon mends the wound that was inflicted on Roran by a Ra'zac in Carvahall as they are camping. Together they infiltrate the fortress and are ambushed by the Ra'zac. Roran kills one of the Ra'zac while the other manages to escape into the depths of Helgrind. Roran rescues Katrina while Eragon finds Sloan, Katrina's father and a traitor to Carvahall, imprisoned. Eragon decides to remain in Helgrind to kill the remaining Ra'zac and deal with Sloan. He tells Saphira to go back to the Varden with Roran and Katrina, which she does reluctantly. Eragon finds and kills the last Ra'zac with ease. Eragon then leaves Helgrind with Sloan and, using Sloan's true name, commands him to travel towards the elves' domain, and Eragon heads back to the Varden. Meanwhile, Saphira arrives at the Varden's camp without Eragon, so Arya sets off in pursuit of him. Arya finds Eragon traveling south in Eastcroft, and they escape to the Varden together. At the Varden's camp, Eragon fixes the curse he accidentally set upon Elva. He also pays his debt to Gedric, from whom he stole hides for Saphira's saddle, and he then visits Jeod and gives his wife a gift as well.

Murtagh and his dragon, Thorn, attack the Varden shortly after Eragon's return, with a unit of soldiers. Elven spell casters aid Eragon, forcing Murtagh and Thorn to flee. After the fight, Eragon binds Roran and Katrina together in marriage. Then Nasuada orders Eragon to attend the election of the new dwarf king, insisting Saphira stay behind, which Eragon reluctantly agrees to. Among the Dwarves, Eragon is reunited with Orik, the clan chief of Durgrimst Ingeitum. An attempt to kill Eragon is found to be the work of the clan Az Sweldn rak Anhûin, who are hostile toward Eragon. Orik presents evidence to the clan-chiefs, who banish the Az Sweldn rak Anhûin clan into exile. Having won the trust of the dwarves, Orik is elected the new dwarf king. At Orik's coronation, Saphira mends Isidar Mithrim, which Arya had shattered while rescuing Eragon from the Shade, Durza.

Eragon and Saphira decide to return to Ellesméra to continue their training. Eragon is told by Oromis and Glaedr that Morzan is not his father; Brom is. The next day, Eragon is told the source of Galbatorix's power; an Eldunarí, or a heart of hearts, is a dragon's heart, which contains their consciousness and exists forever. Glaedr explains that Galbatorix controls hundreds of these, which are the source of his power. They discuss Eragon's need for a new sword as well. Eragon visits Rhunön, the elven blacksmith, whom he asks to forge a new blade for him. She agrees, only after he retrieves the material needed, brightsteel, and Rhunön forges the sword through Eragon's mind and with Eragon's limbs, thus circumventing her oath. Eragon names the sword "Brisingr". When Eragon sets off to return to the Varden, he finds that Oromis and Glaedr are departing as well. Oromis explains that the time has come to oppose Galbatorix alongside Islanzadí. Glaedr gives his Eldunarí to Eragon and Saphira before they part.

Eragon and Saphira return to the Varden, who are engaging in a siege of the city of Feinster, and are reunited with Arya. Eragon and Arya find the leader of the city, Lady Lorana, but discover that her three magicians are attempting to create a Shade. Eragon and Arya race to kill the magicians, as they transform a man into a Shade. Eragon passes out as Glaedr's Eldunarí depicts Oromis and Murtagh fighting, as Oromis suffers a seizure and dies. Eragon watches as Glaedr is killed by Thorn afterwards. As Eragon regains consciousness, he and Arya fight the Shade, Varaug, who falls to the duo. After the successful siege, Nasuada informs Eragon that the Varden plan to march to Belatona, then to Dras-Leona, then to Urû'baen, where they plan to kill Galbatorix.

Courtesy of Wikipedia