Robin Redcap was an especially malevolent Redcap from English folklore and the supposed Familiar of the infamous Lord William de Soulis.
According to the local legends Robin Redcap, along with his master, were responsible for all manner of depravity and devil-worshipping in the past and became so dangerous that the locals had to stage a rebellion of sorts against William de Soulis and boil the madman alive to stop his reign of terror.
As for Robin Redcap himself, the demon was said to have vanished shortly after the death of his master though its never truly known if such a being could ever truly be considered dead - perhaps he is simply waiting for a chance to return.. (in some versions Robin can be seen infrequently, guarding a hidden treasure buried deep under the castle - which he amassed during his reign of terror)
Robin Redcap is likely related to other roaming spirits in English mythology and may well be an alter-ego of said beings, indeed when his master died it is possible Robin Redcap simply took on another form and name, as was common for malicious "fairy folk".
