I googled, because I've been to see this and wanted to tell you about him:
"The Cerne Abbas Giant or the 'Rude Man' is the largest hillfigure in Britain, (the figure's gender is beyond doubt) and he is one of two representations of the human form, the other being the Long Man of Wilmington in East Sussex.
The giant, carved in solid lines from the chalk bedrock measures in at 180 feet high, and carries a huge knobbled club, which measures 120 feet in length.
The first written record of the giant appears in 1751 in a letter by Dorset historian John Hutchins, he suggested that the figure was cut in the mid 1600's. Another slightly later reference to the figure can be found in the Gentleman's magazine of 1764, where the figure is described and depicted with a navel, that has long since disappeared. The lack of earlier references is frustrating but does not mean that the figure dates to the 17th century, and its style and proximity to an Iron Age earthwork suggests a much earlier origin.
There are numerous theories as to when and why the giant was created, one of the more popular is that he is the Greek-Roman god Hercules, who is often represented with a club and an animal fur. It has been suggested that the figure was once depicted carrying and animal fur in his left hand. It is possible that worship of Hercules arrived in the early part of the Roman invasion, which was then became amalgamated with a god of a local Celtic tribe. The theory given the most weight by historians is that it was created during the reign of the Emperor Commodus between 180 - 193 AD, he believed himself to be a reincarnation of Hercules and allowed the cult to revive.