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 de Normanby, 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. de Rigby 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.
After the Percys defeat, de Normanby gave up his regency, but Henry IV wisely returned power to de Normanby and the Abbot of Cronk, making then joint Governors of the Island, and also made de Normanby the first Earl of Sodor and granted him control of Ulfstead Castle. This act showed Sudrians that he respected their former Regent, and that through him he appreciated their patriotism and their worth. It was this gesture which brought the Resistance to an end, and attached Sodor to the English Crown.
Sir Arnold's descendants still hold the Earldom of Sodor, though the family name would eventually change to Norramby.