Ranulf de Glanvill was a notable English lawyer and judge in the 12th century, serving under King Henry II. He is best known for his work on the legal text called the "Treatise on the Laws and Customs of England," which laid the groundwork for common law in England. Glanvill held the position of Chief Justiciar, effectively acting as the king's chief legal officer. His contributions helped to systematize legal procedures and improve the administration of justice during a time of significant legal reform in England.