Avranc was once a man under Manthor's authority, who was a lord of the Haladin. When Manthor's company came across Húrin Thalion near Haudh-en-Elleth, after the death of Morwen, Avranc broke Manthor's command by running ahead to the house of Hardang the Chieftan, without leave, to tell Hardang of Manthor's bringing Húrin to him.
Hardang later made Avranc a Captain of Brethil during the time of Húrin's imprisonment there. When a battle broke out after the 301st Folkmoot of Judgment, at which Húrin was put to trial for his wrongdoings against Hardang, Manthor and Avranc were enemies. In the end, Avranc wounded Manthor with an arrow, and managed to escape. After Húrin's departure from Brethil, Manthor died.
Farang and Faranc were two names Tolkien rejected for this character.