I’ve mentioned redcaps before, but for spooky season, here’s a little about a specific one.
Scottish nobleman William de Soulis was said in folklore to have a redcap familiar called "Robin Redcap". This entity was said to have wrought much harm and ruin in the lands of his master's dwelling, Hermitage Castle. Ultimately, William was (according to legend) taken to the Ninestane Rig, a stone circle near the castle, then wrapped in lead and boiled to death. In reality, William de Soulis was imprisoned in Dumbarton Castle and died there, following his confessed complicity in the conspiracy against Robert the Bruce in 1320.
Sir Walter Scott in Minstrelsy of the Scottish Border (1802) records a ballad written by John Leyden entitled "Lord Soulis" in which Redcap has granted his master safety against weapons and lives in a chest secured by three strong padlocks. Scott states that the redcap is a class of spirits that haunts old castles, and that every ruined tower in the south of Scotland was supposed to have one of these spirits residing within.