Ladislaus III was King of Hungary and Croatia between 1204 and 1205. He was the only child of King Emeric. Ladislaus was crowned king upon the orders of his ill father, who wanted to secure his infant son's succession. The dying king made his brother, Andrew, regent for the period of Ladislaus's minority. However, Duke Andrew ignored the child's interests. As a result, Ladislaus's mother, Constance of Aragon, fled to Austria, taking Ladislaus with her. Ladislaus died unexpectedly in Vienna.

The King of Hungary was the ruling head of state of the Kingdom of Hungary from 1000 to 1918. The style of title "Apostolic King of Hungary" was endorsed by Pope Clement XIII in 1758 and used afterwards by all monarchs of Hungary.