Saint Katherine
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Saint Katherine Elysius was a canonized Living Saint of the Sisters of Battle.
Her rise to prominence coincides with the reforming of the Sisters of Battle as a militant force that was not bound to a very blatantly evil man, as she served as second-in-command to Alicia Dominica, the executor of said evil man, and even got to see the very thing they should have been worshiping.
She eventually formed the Order of the Fiery Heart and led them across the galaxy in a great many genocidal campaigns. It was at this point that she was canonized and discovered some very powerful gear (The Armour of Saint Katherine and the Ardent Blade).
She was eventually slain by a coven of witches, and her order renamed itself as the Order of Our Martyred Lady. Unfortunately, she didn't get to inherit the functional immortality afforded to Saint Celestine.
Triumph of Saint Katherine
One of the most curious additions to the 8th Edition Sisters of Battle Codex was the introduction of the "Triumph of Saint Katherine". Fluff describes it as a funeral procession for Saint Katherine crossed with an elite squad of warriors, empowered by the spirit of the saint as well as those of her fellow Matriarchs.