Maurice was the original bearer of a unique Crest that uses his name. It is said that he was among the original elites who assisted in defeating Nemesis. He alongside Seiros and the Ten Elites were celebrated across Fódlan as a result. Sometime after that, he overtaxed his crest and the sword, Blutgang, causing him to transform into a Demonic Beast. Taking residence in a forest and losing control of his current body, his beast form began killing any individual foolish enough to enter the forest in a gruesome manner. The attacks and knowledge of his transformation ousted him of his acclaim in the war against Nemesis. Maurice would have descendants of his own, but all inheritors of his crest were believed to be cursed, thus his Crest was renamed "The Crest of the Beast". Rumors began to circulate that any descendant of Maurice would transform into "The Beast" that stalks the forest and kill anyone under the influence of him.
Even after 1000 years, his involuntary attacks did not stop, leading to his latest descendant, Marianne to be the target of ire for his actions. Thanks to Byleth and her classmate's assistance, Marianne is able to quell his beast form, retrieving Blutgang and ending his suffering.
Maurice derives from the Roman name Mauritius. It's of latin origin, and means "dark, Moorish"