King Charles I was the only King of England to be executed.
The strict religious views that he imposed on his subjects and his battles with parliament didn't make him terribly popular.
The Scots in particular weren't too happy about this, especially when he tried to force a new prayer book on the country.
It all ended rather badly for Charles when he was executed in 1649 after a reign of twenty four years.
The English civil war society re-enact the period in his memory. They laid a wreath outside Banqueting House, the spot where King Charles was executed. This was followed by a sombre march down the Mall.