euphrati keeler
Euphrati Keeler was originally a Remembrancer during the final days of the Great Crusade aboard the Warmaster Horus' flagship Vengeful Spirit who would go on to be accalimed as the very first saint of the Imperial Cult.
Her experiences in the latter days of the Great Crusade transformed her from a normal young woman with no special abilities into a devoted believer in the divinity of the Emperor of Mankind, a faith so deep that it would prove to be a supernatural bane to Daemons and other servants of Chaos.
After the Horus Heresy began, Keeler would be recognised by others who shared her beliefs as a Living Saint, and the prophet of the Emperor. This reputation would see her later canonised as one of the first saints of the Imperial Cult and the Ecclesiarchy after the establishment of the Imperial state church in the mid-32nd Millennium.