In Scottish border folklore, the malevolent fairy known for a red cap is the redcap.
A redcap, also called a powrie, is a murderous goblin associated especially with ruined castles and towers along the Anglo-Scottish border. Folklore says that it soaks its cap in the blood of victims, keeping the cap vividly red. Stories describe the creature as short and heavily built, with talon-like fingers, fiery eyes, iron boots, and a pikestaff.
Redcaps were thought difficult to defeat by physical force. Traditional accounts instead say that Scripture or a crucifix could drive one away, causing it to vanish in flames. The folklore is closely tied to places associated with tyranny, violence, or other wicked deeds.
A common mix-up is treating every “redcap” as the same creature. Cornwall used “red-caps” more broadly for some fairies, while Dutch redcaps are closer to household gnomes. In Scottish legend, Robin Redcap was a familiar spirit linked to the historical nobleman William de Soulis, but that character is a particular legendary figure rather than the general creature type.