Complex sentence: The name "Swing Riots" was derived from the name that was often appended to the threatening letters sent to farmers, magistrates, parsons, and others, the fictitious Captain Swing, who was regarded as the mythical figurehead of the movement Horspool.
Split into simpler sentences: The name "Swing Riots" was derived from Captain Swing, the fictitious name that was often appended to the threatening letters sent to farmers, magistrates, parsons, and others. He was regarded as the mythical figurehead of the movement Horspool.