William I (c. 950 – after 29 August 993), called the Liberator, was Count of Provence from 968 to his abdication. In 975 or 979, he took the title of marchio or margrave. He is often considered the founder of the county of Provence. He and his elder brother Rotbold I were sons of Boson II of Arles and his wife Constance, who, based on her name, has been speculated to be daughter of Charles Constantine of Vienne. They both carried the title of comes or count concurrently, but it is unknown if they were joint-counts of the whole of Provence or if the region was divided. His brother never bore any other title than count so long as William lived, so the latter seems to have attained a certain supremacy.