William de Ros, Lord of Helmsley, was an English noble.
He was the eldest son of Robert de Ros and Isabella Mac William.
With his father he opposed King John of England, during the First Barons War between 1215 and 1217.
William was captured during the battle of Lincoln on 19 May 1217 and became a prisoner, before paying 20 marks to be released into his fathers care in October 1217.
He married Lucy FitzPeter, the daughter of Peter FitzHerbert and Alice FitzRoger, they are known to have had the following issue:[1]