From The Heretic Knowledge Vault
Marius is a half elf and resident of the sanctuary city of Snamish, where he serves on the town council. He's elderly even by half-elf standards, and is showing physical infirmities to match, reminding us that while elves may be immortal, their half-human progeny are not. An important point about Marius is that he's the natural son of player character Drusia Valis, an elven Peregin who, like Sarine in the main story, was on the pro-half-elf side in the Errant War and founded Snamish as a Santuariel-like place for half elves to live in safety. Marius isn't the only Snamishite who's descended from Drusia, by any means; check the Snamish page for more.
He enters the story when an unfortunately flawed birth to young, half-elven Snamishite Kera Kondriel forces the town to confront the possible arrival of an Errant -- and Errant births in Snamish simply cannot be tolerated. This coincides with the arrival in town of PCs Sister Rose, Lillith, Maduin, etc., as they wander through Veracia on various missions, and it leads to Rose getting dragged into the problem of what to do about the birth, along with Drusia's daughter (and therefore Marius' much younger half sister), the priestess Desiree, who attended at the birth. Marius, a traditionalist, is the most vocal member of the town council calling for the infant to be euthanized, to Rose's (and also Lillith's) horror, and Desiree's (and most everyone else's) painful uncertainty. Alas, the fears that the young Kondriel may have Errant-like defects prove to be realized, and he's quietly and mercifully killed. Marius, stubborn old goat that he is, walks the walk, it must be admitted; after a stinging rebuke by Rose, he mans up and leads a small party to the Kondriel house to administer the lethal dose of a morphine-like substance to the child. In the event, Drusia intervenes and does the grisly deed, and the group moves on to their next adventure, sadder and not necessarily wiser.
Presumably he's still there, grousing at the town council whenever hard problems come up that may defy tradition, and if the action ever returns to Snamish, he'll have to be dealt with again. Incidentally, note that although Marius and Desiree are half-brother and half-sister, at no time do they hint at any personal warmth toward each other as a result.