John Hadley is Remy "Thirteen" Hadley's father, as well as the father of Remy's older brother and Amy Hadley. He appears briefly in a flashback in Let Them Eat Cake (where he is portrayed by actor Christopher Stapleton), but is otherwise an unseen character.
John appears to have moved around a lot as Remy went to several high schools while growing up. He also appears to have been fairly well off as he was able to send Remy to Sarah Lawrence College, the most expensive undergraduate school in the United States.
He was very devoted to his late wife Anne Hadley, who eventually passed away from Huntington's disease. However, during his wife's illness he started an affair with another woman. After Anne died, he married the woman, who became Remy's stepmother.
We learn in Lockdown that John is unaware both of his daughter's bisexuality and the fact that it has been confirmed she has Huntington's disease.