William Otto, Lord of Arkel c. 1385 – 1 December 1417 in Gorinchem was the male member of the House of Arkel. He styled himself Lord of Arkel, although his father had lost control of Arkel in 1412, and William's attempt to regain it, failed. He positioned himself as a potential successor of the childless Duke Reinald IV of Guelders and Jülich; however, this attempt was also unsuccessful.
He was the only legitimate son of John V and his wife Joanna of Jülich. His sister, Maria van Arkel married John II, Count of Egmond. In 1406, the city of Gorinchem asked him to lead their revolt against his father. He does so, but after manipulations by both sides, he leaves Gorinchem and sides with his father again. At the end of the Arkel War, Count William VI of Holland captured Gorinchem and William of Arkel fled to Brabant.
In 1417, William made an attempt to recapture Gorinchem. He laid siege to the city. William and his Cod allies managed to enter the city. However, in the narrow streets around Revetsteeg, he was mortally wounded. He died on the spot.
William had no legitimate children.