I mentioned, over in the Primary and Secondary sources thread, that my favorite part of the first half of Harriet O'Brien's Queen Emma and the Vikings detailed the several stories about how and why Cnut had Eadric Streona executed.

O'Brien describes Eadric as "nefarious"; "streona" ostensibly means "the acquisitor," and he was Ealdorman of Mercia under Aethelred. However, as the Danes came closer to conquering the country, he switched sides several times and murdered several prominent people. It seems that the side he was on was mostly, at any given time, his own.

After Cnut and Edmund Ironside, Aethelred's most likely-looking and deserving heir, had settled to split the country (with Edmund taking Wessex and Cnut taking everything else), Edmund was murdered. The murder was supposedly engineered by Eadric, either on Cnut's orders, or as an attempt to curry favor with him. Either way, Cnut at first reaffirmed Eadric's position as Ealdorman or Jarl of Mercia... then, after a brief period, executed him. This is what O'Brien writes:

Stories of Eadric's execution are recounted with delight by many chroniclers, and it is in tones of distinct satisfaction that [the author of a chronicle commissioned by Queen Emma] dwells on this episode. He maintains that when Eadric demanded rewards for his war deeds Cnut majestically summoned Eric the Norwegian and said, 'Pay this man what we owe him: that is to say, kill him, lest he play us false.' Eric, as a good Scandanavian warlord, immediately raised his axe and neatly chopped off Eadric's head with a mighty blow. Henry of Huntingdon, writing some hundred years later, drew from different sources with his version of events. Eadric's execution was, Henry claims, the direct upshot of his involvement in the murder of Edmund Ironside: when Eadric proudly reported this act to Cnut, the new king apparently rejoined, 'For this deed I will exalt you, as it merits, higher than all the nobles of England.' And he promptly ordered that Eadric be decapitated and his head 'placed upon a pole on the highest battlement of the tower of London' - although the allusion to such a building in London at this date is probably anachronistic.

Apocryphal, but interesting and entertaining. Also worth remembering is that Cnut would have been around eighteen at the time that he captured the throne of England and wisely got rid of Eadric.