The Pack encountered the skeletal horse and rider many times on their journey, eventually dubbing him the "Bonerider". Along the way, the skeleton dropped a Bag of Holding, a Divinatory Diary, and an ancient bottle from the Wizard of Wines, once bound for Castle Ravenloft.
Ciril Romulich was the Father of the Church of Barovia and personal minister to the von Zarovich family. A powerful Cleric of the Morninglord, he was loyal to Count Barov von Zarovich, and remained in the village until Castle Ravenloft was nearing completion. Strahd von Zarovich elevated him to become the High Priest of the entire valley.
Father Romulich presided over the centralization and consolidation of all the churches and established the Morninglord as the supreme divinity in the valley, but he was also fantastically corrupt, looting much of the churches’ wealth for his own personal use. He ignored Strahd’s excesses, pardoned his sins, and blessed his war against the Order of the Silver Dragon. Despite Ciril's immorality, Strahd was reluctant to pursue the intricacies of immortality or the secrets of the Amber Temple too openly while his parents’ favorite priest lived.
During the ill-fated Wedding That Never Was, however, everything changed in an instant. Strahd murdered the Ciril and tried to raise him as a Vampire Spawn, stealing his holy symbol in the process. The Morninglord intervened, and divine power surged through Ciril’s dying body into the holy symbol, transforming it into the Icon of Ravenloft. Preserved from Strahd’s curse yet still alive in some way, Ciril escaped the castle on horseback as Strahd’s fought off guards and chased Tatyana Federovna.
He died from his wounds as he made his way to the Black Carriage Crossroads, but the spirit of the cleric and his horse lingered. Over centuries, High Priest Ciril became a fixture on the Old Svalich Road, wandering without sentience or purpose but never deviating from his path. Reduced to a near-mindless Skeleton in rusted chain mail atop a Skeletal Horse, they trotted along, bearing a broken lantern that produced no light. However, he had enough sentience to occasionally collect items, which he would give to others to use as they rebelled against Strahd.
Though only Strahd knew of Ciril's past, he gained a reputation amongst Adventurers as a non-hostile encounter on the road who seemingly ignoring all living beings, but dropped esoteric items behind them.