Hamo was the son of Hamon Dentatus, a Norman noble who held the lordship of Torigni-sur-Vire near Manche in Normandy.
[6] The historian Emma Mason suggests that Hamo, along with Ranulf Flambard, Urse d'Abetot, Robert FitzHamon (Hamo's son), Roger Bigod and Eudo Dapifer, were the first recognisable Barons of the Exchequer under William II.
[9] Hamo's involvement in the higher levels of government dates especially from King William II's absence from England in the late 1090s.
[10] In 1099, when William II was in Normandy, Hamo was one of the main assistants to Flambard, who had been left as regent of England in the king's absence.
[3] Robert was probably the elder, as he received his father's lands in Normandy after Hamo's death.