Dimintheis Fitzharmon is a non-player character and a noble of Varrock. He is featured heavily in the quest Family Crest. He is the father of Avan, Caleb and Johnathon Fitzharmon. His house is located south of Varrock's east gate, north of the Fancy dress shop in the fenced off area.
You must talk to him to start the Family Crest quest. He lives in the fenced-off area in the south-east corner of Varrock. He had given each of his 3 sons pieces of his family crest. He must get it back to regain his place in Varrock.
When you complete the quest, he gives you steel gauntlets that can be enchanted into chaos gauntlets, goldsmith gauntlets, or cooking gauntlets. He returns them to you for free if you ever lose them. Note that only his sons are able to change the type of your gauntlets.