The monarch we spend the most time with in this film is John Lackland, later King John. John was a Plantagenet, son of Henry II and Eleanor of Aquitane. He was born on Christmas Eve 1166. He was the youngest of five sons and so never expected to rule. However, when Princes William, Henry and Geoffrey died young and Richard I became king in 1189, John became potential heir to the throne. This film takes place after Richard I has left to command the Third Crusade, leaving Chancellor Longchamps as regent. When the film opens, John has already outmaneuvered Longchamps and installed himself as regent.
Prince John is played by the great Claude Rains (1889-1967). Rains would go on to play other royal characters: Napoleon III (twice), Julius Caesar and the biblical King Herod. In addition to acting, Rains was also highly sought as an acting teacher. Among his students were Laurence Olivier and John Gielgud, who would themselves go on to play many monarchs.
John is often painted as a detestable villain (especially in re-tellings of the Robin Hood legend) but history records that he was a strong general and an able administrator. He did, however, have some very unpleasant personal characteristics which made him an unpopular king. He was reportedly arrogant and petty and also dangerously cruel. I think Rains does a good job of capturing John's vanity and arrogance in this performance.