Felix is a vampire member of the Volturi guard, but possesses no other special talent than his superior physical capabilities. His motivations are unknown, and the only clues to discern his character are his physical actions and his talks to Bella and Edward.
Little is known about Felix's history other than that he was created by Aro and had been within his guard for centuries. He is kept within the guard due to his battle techniques and superior strength that made him frightening to their enemies. Though he wears the lighter gray cloak of a lesser member of the guard, he does maintain a permanent position, because he is the strongest vampire the Volturi have encountered.
Throughout the centuries, Felix has been a part of most of the Volturi's punitive missions. When there are larger threats, he is often accompanied by other physically dominant members, like Santiago, or other transitory guard members to eliminate them.
In New Moon, Felix helps to hold members of the Cullen family while Aro, Caius, and Marcus deliberate on the decision on what to do with Alice, Bella, and Edward. His wanting Bella to stay in Volterra angers Edward.
In the film adaptation, Aro orders Felix to kill Bella due to her knowledge, but Edward refuses and they start a fight, with Felix winning, and almost killing Edward until Aro orders him to stop.
The Short Second Life of Bree Tanner
In The Short Second Life of Bree Tanner, Aro sends Felix, Jane and two other members to Seattle, Washington after a series of mysterious and conspicuous murders began to commit. Jane confronts Victoria and Riley with three other guards and gives them a five-day limit to fulfill their army's purpose. Among them is Felix.
In Eclipse, Felix and the others enter the battle site where the Cullens fight the newborn army after the battle. At the end of the battle, he moves in to confront the Cullens, and determine, along with Jane, what to do with them after what happened. It is also Felix that burned Bree after the Volturi decided to "dispose" of her. When he was ready to dispose of Bree, however, the Volturi stopped him and decides to spare the newborn. In the end Bree survived and the Volturi left the Cullens.
In Breaking Dawn, Felix travels to Forks with the Volturi after Irina reported the Cullens' creation of an immortal child, which later turns out to be a great misunderstanding. Felix expresses sadness with the thought of killing Bella, whom now has taken immortality. While Aro interrogates the Cullens' witnesses, Felix was one of three guards to protect him. He returns to Volterra with his coven after the confrontation ended "peacefully".
After returning to Volterra Felix met and impreganted a human female under commands of the Volturi. In the end she successfully gave birth to a half human, half vampire daughter named Olivia. A month later, Felix found her feeding off her mother and brought her to the Volturi where she met Damien, another hybrid and the two quickly became friends. Seven years later, when the final conflict with the Cullen family accured, Felix was one of the Guards that was in the battle. Felix was the one who destoryed most of the Newborns. Vampires and Children of the Moon (in human form) alike. However, Felix met his end at the hands of one of the newborn werewolves, Jayden Noel, had fled away from the fight and Felix immediately went after her. This would prove to be his fatal mistake. In the end Felix never returned back to Volterra, and his scattered remains eventually were discovered by the Cullen family, signaling he met his end at the hands of the Werewolf he tried to pursue.
Felix is described by Bella as "very big, tall, and thick through the shoulders", and that his size reminds her of Emmett Cullen. He is also described as having a slightly olive complexion which looks odd combined with his chalky pallor. He also has short, cropped, black hair, though in the film portrayal, Felix has dark brown hair that is layered. He has the red eyes of a vampire that drinks human blood. The guard member is about 6'7" and is very strong. He is not gifted, unlike most of the Volturi. It is assumed that he is kept in the guard because of his immense strength and physicality. He also is thought to be a fighter, because of his eager optimism at the possibility of a fight.
In Breaking Dawn, Bella meets Felix again, describing him as hulking and menacing as an iron-spiked cudgel.
In New Moon, he is seemingly disappointed when Bella doesn't stay in Volterra, and Edward seems annoyed by his infatuation with her. In Eclipse, when the Volturi finally notice the chaos, he winks at Bella. In Breaking Dawn, he compliments Bella's "new face" and says, "It's too bad....". Although he trails off, Bella assumes he was about to say that it was too bad that they were going to have to kill her. Bella, then, sarcastically agrees; and he winks, yet again. He is somewhat of a comedian and a flirt, and in New Moon, Bella sees him wink at Gianna, the Volturi's human-later-turned-vampire secretary, who responds by giggling.
It seems he is very good friends with Demetri.
Powers and abilities
Meyer stated that Felix's talent is his fighting abilities and physical strength (comparable to Emmett Cullen). No matter how good anyone else is in physical combat, Felix will always remain one, or most likely, several steps ahead of them. He can also anticipate his opponent's moves to counter attack them. Coupled with his large size and muscular build, Felix is known as the most physically powerful vampire the Volturi have ever discovered.
The most probable way to defeat such a powerful vampire is to utilize a powerful, long-ranged supernatural talent, as demonstrated by Jane, but it was possible to defeat him through hand-to-hand combat because a newborn werewolf named Jayden Noel had been the one who finally slayed him.