Nahuel is described to beautiful, with dark skin and long dark hair tied in a rough braid. He has not the red eyes of vampires, but warm teak eyes, probably his human mothers, Pire.
A century and half earlier, Hulien and her sister Pire lived with the Mapuche tribe. Pire was a very beautiful woman and one day told her sister about an 'angel' that found her in the woods and used to visit her during the night. Hulien knew that this 'angel' was a vampire, and warned her sister. But she did not listen and soon Pire discovered she was pregnant with a vampire child. Knowing that the Mapuche people would want to destroy the child, Pire and Hulien ran away to the deepest part of the forest.
Hulien cared for her sister during her dangerous pregnancy, by hunting for her and trying to keep her alive through the hard time. Pire had to drink animal blood to keep her and Nahuel alive during the pregnancy.
Hulien wanted to kill the monster child, but Pire loved the vampire child growing in her womb, even when the child grew strong and broke her bones. She named him Nahuel, after the jungle cat. Hulien was unable to save her sister's life when Nahuel ripped his way free of his mother's womb, killing her quickly.
Soon after, Nahuel bit Hulien, injecting her with his venom, and turned her into a vampire. Nahuel's father, a vampire named Joham, came looking for him a few years later wanting his son to join him. Joham believes he is creating a super-race with human/vampire children. Nahuel is Joham's only son. He has three other hybrid daughters, and raises them to think of humans as animals. Nahuel does not like his father and refused to join him, as he already has a family with Hulien.
Nahuel was sad about his family. He was happy to have Hulien, but thought his father should be a better person and that his mother deserved life. He also saw himself as an evil creation because his birth killed his mother.
 Breaking Dawn
Nahuel and Hulien were recruited by Alice and Jasper, and brought to Forks to testify against the Volturi. Nahuel's testimony is critical in convincing them that Renesmee is not a threat, and after the confrontation, Nahuel and Hulien were one of the last to leave.