Dehaan was born into the retinue of the Setite traveler Ankhesenaten (known to Europeans as Andreas Aegyptus) and raised to revere Set as the one true god, even in the largely christian Flanders. When he turned ten, he chose to follow his master's caravan, to tend to his grandmother, the high priestess Ljudumilu. His grandmother tutored him in medicine and over what moved the hearts of men, as well as parts of Setite doctrine. As all, he was marked by the common symbol of a Setite ghoul – a serpent coiled around the hieroglyphs for Thunder, Set's domain. In Ankhesenaten's travels, Dehaan usually tended to any Cainite passengers that had chosen to not spend their nights in torpor during the journey. While on caravan in 1205, Dehaan met the Setite Meribah and was fascinated by her. At his grandmother's behest, he tested her devotion to the Setite faith, by offering her his blood. Meribah rejected it.
While Ljudmilu saw this as a sign of scorning desire and found her wanting and barely deserving of Set's gift, Ankhesenaten found it appropriate that Dehaan would continue to test Meribah's dedication to Setite doctrine. Dehaan used this to spend time with Meribah, for whom he developed a growing attraction, even against the wishes of his grandmother. When the caravan was stranded in Spalato, Ljudumilu sacrificed herself in a Setite ritual to summon a storm, in exchange demanding that Dehaan would become one of the undead. Ankhesenaten, who had sworn to himself to never have childer, instead let Dehaan try to teach Meribah the basics of the language of Ancient Egypt. During this time, Dehaan noticed Meribah's fear of other members of the Followers of Set, since she was only a desher and had not been fully tutored in the ways of her Clan and came to believe that his master would eventually kill her.
When the caravan was attacked near Chambery by members of the Red Order and Knight Templars in 1208, Dehaan fought to drive them off with the rest of the mortal retinue, but was overwhelmed. Working to free those taken prisoner, he scouted the fortress of the Order during the daylight to allow his Cainite masters to enter. After they managed to flee from the fortress, Dehaan covered their escape. For this deed, Ankhesenaten found a compromise: Dehaan would be Embraced by Meribah and adopted by himself, so that in the eyes of the clan elders, he would have a respected lineage, but not the stigma of a high generation. Dehaan later accompanied both Ankhesenaten and Meribah to Oradea, where they escorted Markus Musa Giovanni to a meeting with Myca Vykos. Here, Dehaan was presented as Ankhesenaten's childe.
Dehaan is described as absurdly handsome, golden-locked, straight-limbed, and strong.