The Order of the Knights of Saint Hagan was a Christian military order during the Middle Ages.
In the Siege of Acre of 1291, Crusader Hagan Douglas, who was greatly regarded by the city's defenders, was captured and tortured by the Mamalukes before being beheaded and sent back to Acre to inflict a morale blow to the Crusaders. At the last battle for the city, Hagan's headless body was resurrected and fought alongside his men. Although the Christians lost the city along with Hagan's body, the forty-seven knights that witnessed Hagan's resurrection survived and escaped. Inspired by the miracle, the knights founded the Order of the Knights of Saint Hagan in honor of the Crusader's namesake and patrolling the Holy Land in hunting the servants of "the evil one". The Knights of Saint Hagan encountered the abode of the demon Asmodeus, and drove away the demon and killing his human wives.
In 1307, Pope Clement V recalled the Knights of Saint Hagan and were dispatched to France to oversee the arrest and trial of the Knights Templar, many of whom they had fought beside. After that, the Knights of Saint Hagan continued as inquisitors. But others, having grown weary of the bloodshed, retired from the Order.
A handful of Knights under William Fitzroy became monks that renounced violence and settled in a chapel that was given by French King Phillip IV for Fitzroy's service against the Templars. However, the former members of the Knights of Saint Hagan were not allowed to live their days in peace, as the vengeful demon Asmodeus discovered them and killed them one by one by dropping them onto the rooftop of the chapel from the sky.
In 1985, a ghost of one of the former knights gained their revenge on Asmodeus through Hellboy, who killed the demon.