It's not that often that the Royal Mint decides to create a coin commemorating something that happened a thousand years ago. It was a coronation of a king of England, so maybe that swayed it a bit. Not an English king, but royalty doesn't work like that anyway.
Surrounded by admirers and sycophants, Canute tried to demonstrate that he was nothing compared to the power of the elements, which were ruled by God. He did this by sitting on his throne by the edge of the sea and demanding that the waves stopped. He commanded the sea not to wet his feet or his clothes, which it did. Henry Huntingdon says: "Then the king leapt backwards, saying: 'Let all men know how empty and worthless is the power of kings, for there is none worthy of the name, but He whom heaven, earth, and sea obey by eternal laws.'" He then hung his gold crown on a crucifix, and never wore it again "to the honour of God the almighty King"."
Throughout the ages however, the story has changed and it is often give as an example of arrogance, as if Canute expected the waves not to wet him because he was the king. But the fact that we still talk about him a thousand years later is recognition enough.