Eadmund (c. 980-1016), called Ironside, King of the English, was the son of Æthelred the Unready by his first wife Ælfgifu of .

In 1015, Eadmund desired to marry Ealdgyth, the widow of the Danish earl , who, along with his fellow earl Morkere, had that year been slain at by . Æthelred, who had seized on the possessions of the earls, and had sent Ealdgyth to Malmesbury, was not willing that his son should make this marriage. Nevertheless Eadmund took Ealdgyth from Malmesbury, married her, and then went to the Five Boroughs of the Danelaw or Danish confederacy, where the murdered earls had ruled, and received the submission of the people. It seems highly probable that this marriage, and the establishment of his power in the Danish district, deeply offended his brother-in-law Eadric, the Mercian earl; for, when Cnut invaded the country shortly afterwards, and Eadmund raised an army to meet him and joined forces with Eadric, a bitter quarrel broke out between them, and the earl, after having, it is said, endeavoured to slay him, went over to the side of Cnut. After this desertion, Eadmund was unable to defend in the beginning of 1016, for his levies declared that they would not fight unless he was joined by the king, who had lately been sick, and by the Londoners. He tried to raise another force, declaring that all who disobeyed his summons should suffer the full penalty, and sent to his father desiring him to come and help him. Æthelred came, did no good, and went back to . Eadmund then retired into Northumbria, joined earl Uhtred, and with his help harried and other parts of eastern Mercia which had submitted to Cnut. Uhtred was compelled to draw off his forces and hasten back to his own earldom, for Cnut was marching on York, and Eadmund joined his father in London about Easter. The death of Æthelred on the 23rd of April 1016 was followed by a double election to the English crown. The citizens of London and those members of the Witan who were present in the city chose Eadmund, the rest of the Witan meeting at Southampton elected Cnut. and at the time of his election Eadmund's kingdom was bounded by the walls of London. In the warfare which ensued Eadmund fought at the severest disadvantage, for his armies dispersed after every engagement, whatever its issue. Cnut at once fiercely besieged London, but the citizens successfully resisted all attacks. Eadmund meanwhile marched through Wessex and received its submission. At Pen in Somersetshire he engaged the Danes and defeated them. Cnut now raised the siege of London and soon afterwards encountered Eadmund at Sherston in . Eadmund, who was called Ironside for his bravery, was now at the head of troops raised from Devonshire, Dorsetshire, and Wiltshire, while Cnut had in his army levies from Hampshire and other parts of Wiltshire, so that Eadmund had now extended his kingdom so far east as to take in some parts of Wiltshire. The fight began on a Monday, and Eadmund, who had placed his best warriors in the front line, stood with them and fought hand to hand with the enemy. When evening came the two armies, wearied with battle, drew off a little from one another. The next day they renewed the fight, and the army of Eadmund had, it is said, gained a decided advantage, when Eadric Streona discouraged the English by holding up a head which he declared to be the head of their king. Eadmund, we are told, got upon some mound, took off his helmet that his men might see his face, and then with all his strength hurled a spear at Eadric, who warded it off; it glanced from his shield, struck the soldier who was standing by him, and pierced him and another man also; such was the tradition as to his strength in the twelfth century. The battle again lasted till twilight, and again both armies fell back from each other, but though the issue was undecided Eadmund reaped the fruits of victory, for in the stillness of the night Cnut drew off his forces and marched back towards London, where he again pressed the siege, thus leaving Eadmund undisputed possession of Wessex. Eadmund hastened after him and relieved London. He defeated the Danes at Brentford and again at Otford, and drove them into Sheppey. Eadmund was now joined by Eadric, in conjunction with whom he followed the Danes into , overtaking them at Assandun (or Ashingdon). In the battle which took place, Eadric again played the traitor, and the English were routed with terrible slaughter. According to Henry of Huntingdon, after this defeat Eadmund went into Gloucestershire, and there for the seventh time began to gather a fresh force. Cnut followed him, and although Eadmund was anxious to make another attack upon the enemy, Eadric and other nobles refused to allow him to do so, and arranged that the kings should hold a conference and divide the kingdom between them. This conference was held on an island of the Severn, called Olney. The two rivals swore friendship, and a division of the kingdom was effected—Cnut taking the north, Eadmund the south. Soon afterwards Eadmund died (30th of November 1016), probably from natural causes, though later historians hint at foul play. He left two sons, Eadmund and Eadward the Exile, and was buried with his grandfather Eadgar at Glastonbury, before the high altar. After the death of Eadmund, Cnut was unanimously elected king of all England at the beginning of 1017, as is attested to in the later anonymous Elizabethan drama, : Act I, scene 1. Countrymen: Where is the king, that he may right our wrong? Canutus: The king is here; who is it calls the king? I am your king. Speak, gentle countrymen, what lawless hand hath done you injury?

Eadric was again the earl of Mercia, but when he was in London the Christmas of 1017, he was slain in the palace by the king's orders, ‘very rightly,’ because Cnut feared that he might act toward him as he had acted to his former lords, Æthelred and Eadmund. His body was thrown over the wall of the city, and was left unburied.