Stephen Kellner is Darius’s father, a man Darius calls Übermensch because of the ease with which he seemingly breezes through life despite dealing with depression. Stephen’s depression, like Darius’s, requires medical treatment, yet Darius sees his father as being in control of his depression without struggling the way Darius feels he does. This disheartens Darius, and his relationship with his father is strained as a result. It’s only when Stephen opens up authentically and vulnerably with his son that both can begin healing their own wounds and connect on a deeper emotional level.
With his son, Stephen is secretly ashamed of his own debilitating depression and is devastated that he's passed his depression down to his son. Thus, Stephen makes efforts to guide Darius away from self-sabotaging thoughts and behaviors. However, because Stephen fails to explain his motives, his words and actions only alienate him from his son further. For instance, Darius’s misconception that Chip has bad intentions causes him to push Chip away at the beginning of the novel, but when Stephen tells Darius that this was likely a misunderstanding, Darius feels dismissed. In reality, Stephen can see that aspects of Darius’s depression are causing his son to reject necessary friendships, but rather than counseling him honestly, he inadvertently creates more conflict. It is not until the family is in Iran and Stephen spends time as the outlier among his wife’s family (even if he’s readily accepted and valued) that he’s able to open up and cry with his son in a therapeutic moment of vulnerability. He admits his fears about Darius inheriting his depression, knowing that he cannot always protect Darius from the world’s evils. Through this exchange, Stephen learns that he can best help Darius protect himself by being more open and less critical.