The Bloody Baron is the resident House Ghost of Slytherin at Hogwarts School of Witchcraft and Wizardry. A gaunt and terrifying spectre covered in silvery blood stains, he is known for his silent, menacing presence. In life, he was a wizard who attended Hogwarts during the era of the founders. His tragic history is deeply intertwined with that of Helena Ravenclaw (The Grey Lady), the ghost of Ravenclaw House, whose murder at his hands led to his own suicide and subsequent cursed appearance as a ghost. He is one of the few beings, along with Albus Dumbledore, whom Peeves the Poltergeist genuinely fears.
The Baron lived in the late tenth and early eleventh centuries and attended Hogwarts as a student in Slytherin House. During this time, he fell in love with Helena Ravenclaw, the daughter of Hogwarts founder Rowena Ravenclaw. His affections, however, were not returned. Helena, envious of her mother's wisdom and status, stole her mother's Diadem and fled to Albania. On her deathbed, a regretful Rowena Ravenclaw wished to see her daughter one last time and sent the Baron, who had always loved Helena, to find her, knowing he would not rest until he had done so. The Baron tracked Helena to a forest in Albania. When she refused to return with him, the Baron, who had a fiery temper, became enraged by her rejection and stabbed her. Instantly overcome with remorse for his horrific act, he used the very same weapon to take his own life. Following his death, he returned to Hogwarts Castle as a ghost, forever bearing the ghostly bloodstains of his victim as a mark of his eternal shame. As a form of penance, he also carries and rattles heavy chains. He became the House Ghost for Slytherin and has haunted the castle for centuries, his fearsome reputation growing among students, staff, and fellow ghosts alike.
The Bloody Baron is a horrifying sight. He is described as a gaunt ghost with staring, blank eyes and a haggard face. His most prominent feature is the silvery blood that spatters his robes, a ghastly and permanent reminder of his murder of Helena Ravenclaw. He often makes his presence known by emitting horrifying groans and rattling the chains he chose to wear in the afterlife as a sign of his remorse. His personality is grim, silent, and largely unapproachable. Most Hogwarts students actively avoid him, and even other ghosts seem wary of his presence. Nearly Headless Nick appears uncomfortable when discussing him, stating that the Baron has never been very talkative. Despite his terrifying demeanour, his actions are driven by a deep and unending regret for his past crimes. He exercises his authority over Peeves effectively, often being the only one capable of controlling the unruly Poltergeist.
Little is known of the Baron's magical abilities as a living wizard, though the fact that Rowena Ravenclaw entrusted him with the crucial task of finding her daughter suggests he was competent and resourceful. As a ghost, he possesses the standard supernatural abilities of his kind, including the ability to float, fly, and pass through solid objects. His most significant “skill” in his afterlife is his terrifying aura, which is so potent that it is his primary tool for intimidating others, most notably Peeves. His mere presence is often enough to make the Poltergeist cease his mischief and flee.