Henry III (1216-1272) came to the throne at the age of 9 with the country in the grip of civil war. He was the son of King John. Despite having invited Louis of France to come and take the throne from King John, the English nobles now changed sides to support the young king and Louis was defeated and forced back to France.
The regency - the period before Henry came of age and was allowed to rule by himself, so the country was run by favoured nobles - was a relatively peaceful time. But when Henry took power for himself in 1227, he immediately angered his nobles by ignoring their advice, promoting his friends to positions of power and raising taxes. They made him agree to call a Parliament every 3 years. When he didn't keep his promise, civil war broke out and Henry and his son Edward were captured and imprisoned.
A powerfulk noble, Simon De Montfort, ruled instead. He called a parliament to which important 'commoners' were invited as well as nobles - and this of course was the origins of today's House of Commons.
Prince Edward escaped and defeated Simon de Montfort's forces at the Battle of Evesham in 1265, returning Henry III to power.
Henry III was a very pious man. He was facinated by Edward the Confessor and named his son after him, despite the name being very unfashionable at the time (which is hard to believe now!) He is responsible for the rebuilding of Westminster Abbey in the ornate, gothic style in which it stands today.