Canute I, or Canute the Great also appears as Cnut in the Chronicles of the Anglo-Saxons (Old Norse: Knútr inn ríki, Danish: Knud den Store, Norwegian: Knut den mektige, Swedish: Knut den store; in English also Cnut) (ca. 995 – November 12, 1035) was a Danish king of  England, Denmark, Norway, parts of modern Sweden (including Sigtuna), as well as governor or overlord of Schleswig and Pomerania. He was in treaty with the Holy Roman Emperors Henry II and Conrad II and maintained good relations with the papacy. He ruled a North Sea empire which saw Danish control at its height.

Canute was the son of king Sweyn Forkbeard of Denmark and his queen, the daughter of  Mieszko I, first Duke of Poland. Little is known for sure of his life before 1033. That year, in August, he accompanied his father on his successful invasion of England. While King Sweyn was off conquering England, Canute was left in charge of the remainder of the Danish army at Gainsborough. Upon the sudden death of his father the following February, Canute was proclaimed king by the Danish army. However, the Witan (national assembly of Ealdormen/Earls) refused to accept him and instead voted to restore the defeated king Ethelred the Unready from exile in Normandy.

Ethelred quickly raised an army, forcing Canute to abandon England and sail back to Denmark with the remnants of his army. When he sailed past Sandwich, Canute mutilated hostages given to his father as pledges of support from local nobles.

Canute’s older brother Harold became the King of Denmark on their father’s death. Canute suggested that the two brothers should jointly rule the Kingdom, which found little appeal with his brother. However, Harold promised him assistance and support for his conquest of England if Canute renounced his rights to the Danish throne. Canute kept silent and waited for an opportunity to present itself when he would reclaim his throne in England

Canute proceeded to England in the summer of 1015 with a Danish force of approximately 10,000 men. This time, he was joined by his Norwegian brother-in-law Eiríkr Hákonarson, who was an experienced soldier and statesman. Fortunately for Canute, a strong mercenary chief, Thorkell the High, pledged alliegance to him. The Earl Eadric Streona also joined the Danes with forty ships. The invasion force landed in Essex, which was occupied quickly. Northumbria fell next, and Canute executed its Earl Uhtred for breaking an oath pledged to Sweyn Forkbeard two years earlier.

In April 1016, Canute entered the Thames with his fleet and besieged London. King Ethelred died suddenly during the siege, and his son Edmund Ironside was proclaimed king. When Edmund left London to raise an army in the countryside, he was intercepted by Canute at Ashingdon, Essex. After a decisive victory for Canute in the Battle of Ashingdon, Edmund was forced to negotiate under unfavourable circumstances.

Meeting on an island in the Severn River, King Edmund was forced to accept defeat and sign a treaty with Canute in which all of England except for Wessex would be controlled by Canute, and when one of the kings should die, the other king would take all of England; his sons being the heir to the throne. After Edmund's death (possibly murder) on 30 November 1016, Canute ruled the whole kingdom. Canute was recognised by the nobility as the sole king in January 1017.

In order to associate his line with the overthrown English dynasty and to insure himself against attack from Normandy, where Ethelred's sons Edward the Confessor and Alfred Atheling were in exile, Canute married (July 1017) Ethelred's widow Emma of Normandy, daughter of Richard the Fearless, Duke of Normandy. He duly proclaimed their son Harthacanute as his heir, while his first son, Harold Harefoot (by Aelgifu of Northampton) was on the sidelines. He sent Harthacnut to Denmark while he was still a boy, and the heir to the throne was brought up in Denmark.

As King of England, Canute combined English and Danish institutions and personnel. His mutilation of the hostages taken by his father in pledge of English loyalty is remembered above all as being uncharacteristic of his rule.

By dividing the country (1017) into the four great earldoms of Wessex, Mercia, East Anglia and Northumbria, he instituted the system of territorial lordships which would underlie English government for centuries. The very last Danegeld ever paid, a sum of £82,500, went to Canute in 1018. He felt secure enough to send the invasion fleet back to Denmark with £72,000 that same year.

Canute reinstated the laws passed under King Edgar. However, he reformed the existing laws and initiated a new series of laws and proclamations. Two significant ones were On Heriots and Reliefs, and Inheritance in Case of Intestacy. He strengthened the coinage system, and initiated a series of new coins which would be of equal weight as those being used in Denmark and other parts of Scandinavia. This greatly improved the trade of England, whose economy was in turmoil following years of social disorder.