The Haddingjar refers on the one hand to legends about two brothers by this name, and on the other hand to possibly related legends based on the Hasdingi, the royal dynasty of the Vandals. The accounts vary greatly.
It has been suggested that they were originally two Proto-Germanic legendary heroes by the name *Hazdingōz, meaning the "longhairs", and that they were identical to the Alci mentioned by Tacitus. According to Tacitus, the Alci were worshiped as gods by priests in female clothing:
Cassius Dio mentioned c. 170 the Astingoi as a noble clan among the Vandals, and the Asdingi reappear, in the 6th century in Jordanes' work as the royal dynasty of the Vandals.
The root appears in Old Icelandic as haddr meaning "women hair", and the motivation for the name Haddingjar/Astingoi/Asdingi was probably that men from Germanic royal dynasties sported long hair as a mark of dignity (cf. the "longhaired Merovingians").