His paternal fourth great-grandfather was King David I. Robert's grandfather, Robert de Brus, 5th Lord of Annandale, was one of the claimants to the Scottish throne during the "Great Cause". As Earl of Carrick, Robert the Bruce supported his family's claim to the Scottish throne and took part in William Wallace's revolt against Edward I of England. Appointed in 1298 as a Guardian of Scotland alongside his chief rival for the throne, John Comyn of Badenoch, and William Lamberton, Bishop of St Andrews, Robert resigned in 1300 because of his quarrels with Comyn and the apparently imminent restoration of John Balliol to the Scottish throne. After submitting to Edward I in 1302 and returning to "the king's peace," Robert inherited his family's claim to the Scottish throne upon his father's death.