Captain Rock was a mythical Irish Folk hero, and the name used for the Agrarian rebel group he represented in the south-west of Ireland from 1821-1824. Similar to the earlier Whiteboys, they arose as a reaction against the English and Anglo-Irish Feudal landowners. Captain Rock (or Rockites) were responsible for up to a thousand incidents of murder, arson, rape and mutilation in the short time they were active.
References
Captain Rock Wikipedia(Text) CC BY-SA