Sir Arnold de Normanby was the last Regent of Sodor during the Middle Ages.
Sir Arnold de Normanby was elected Regent of Sodor at some point prior to 1399. In 1399, King Henry IV granted control of Sodor to the Percy family after he had the previous owner, William le Scrope, beheaded. Sudrians, however, did not recognise the Percys ownership and, led by Sir Arnold, they waged a full scale rebellion against the Percys, and were able to prevent them gaining control of the entire island.
In 1404, the Earl of Northumberland, Henry Percy, launched his own rebellion against Henry IV, who sent an emissary, Sir Peter de Rigby, to negotiate with the Sudrians. Sir Peter was favourably impressed by Sir Arnold, and placed himself and his army under the Regent's command, and the Sudrians, having never acknowledged the Percys, cheerfully joined in expelling the Percy garrisons from their Island. Over the course of the campaign, Sir Arnold and Sir Peter developed a considerable liking and respect for each other.
Sir Arnold's descendants still hold the Earldom of Sodor, though the family name would eventually change to Norramby.