Joham is a vampire living in South America, who considers himself to be a scientist creating a super race of half-vampire half-human children. He is an incubus and seduces beautiful women, such as Pire, from their homes and leaves them as soon as they become pregnant. He later attempts to find the children which survive, likely a small number due to the dangers of the pregnancy. He has fathered at least four children, including Nahuel, though likely more as he does not monitor the births. He taught his daughters that they were gods and that humans were animals, leading them to be remorseless.
In Breaking Dawn when The Volturi arrive in Forks to "punish" the Cullens, Nahuel explains that Joham is the person they really should look up.