Henry IV of England (I of Navarre) (1244 - 22 July 1274) was the King of England and Navarre from the death of his brother in 1270. He was known as Henry the Fat.
Henry was born to Theobald II of England and was the younger brother of Theobald III. Due to the family's ownership of two Kingdoms geographically distant from each other Henry acted as Regent for his brother in Navarre from 1262. Unlike his brother, Henry was very friendly with the nobles of both realms and was reluctant to call the Navarrese Parliament, which might have harmed their interests. In 1269, he married into the French Royal Family in readiness for his succession to the throne, when he would have to travel through French territory quite often.
At Theobald III's death returning from a minor Crusade Henry IV succeeded his childless brother as King of both countries. He was basically good-natured and didn't interfere with the working of the formidable English bureaucracy. This, combined with the shortness of his reign, is the reason why the years 1270 to 1274 are almost always forgotten by historians. At one point he offered to send an official army over to Ireland to help the piecemeal baronial conquest that had been going on for nearly eighty years, but that didn't come to anything.
The main issue that Henry IV faced was that of succession. His young son Theobald died falling off some battlements in 1273 and he was left with a baby daughter at his death. This was the end of the male line if the House of Blois, but what was to succeed it? The rules of succession called for the closest adult male relative of the king, and that would have been John II, Duke of Brittany (the son of Henry's half-sister), but the English War of Succession (1215-1222) had made the Anglo-Navarrese fearful of succession disputes. Henry had a young daughter and slightly less young full nephews, not to mention more distant relatives like the Count of Hainaut and Anjou and even the King of France. No didtinct pronouncement was made before Henry IV's death in 1274 so the Duke of Brittany succeeded under the established law, but he was always fearful of his cousins, several of whom he imprisoned.
Henry IV died in 1274, apparently suffocating in his own fat. He was succeeded by his half-nephew, John of Brittany. The immediate result of this was the separation of England from Navarre, which was inherited by Henry's baby daughter, and it's unison with the Duchy of Britanny instead.