Decimus was the older brother of Darius. They come from a former minor noble house of Arthedain, which fell on hard times some decades ago, and lost it's fortunes. It has become a tradition for the young men of the family, upon coming of age, to go out and seek to rebuild their families fame and fortune by adventuring, and great deeds. Decimus knows many of his uncle's, and cousins have gone before him, and is always on the look out for family members.
Decimus and Darius joined Sage, and Kadia in Bree, then the group met the Elves in Caras Marad. After several adventures Darius received a grave wound, which festered. A short while later Decimus was severely wounded. Jolie used rare and poweful magical herbs to revive Decimus, but at that point Darius died.
After burying his brother Decimus continued to adventure with the party. Much later, after the party regained the ring, and began their quest to destroy it, Decimus received a mortal wound in a battle with Orange Men near the Mitheithel River. The party carried his mortal remains on their quest until he was stolen by Gilrion. Raised as undead he was sent against the party in the forges of the Gwaith-i-Mirdain. The party managed to incapacitate him, but it was painfully obvious he was unrecoverable. His remains were returned to Caras Marad and buried with his brother.