To refresh your memory, the mysterious Mr. Mooney is the owner of the bookstore in which Joe works and is often referred to without being actually shown in present day. Flashbacks peppered throughout late season 1 episodes reveal that Mooney (played by Mark Blum) is actually to blame for how twisted Joe has become in his adult life, because of the way he raised Joe during his teen years. Mooney’s idea of mentoring the young boy was actually just mental, and physical, abuse. He often locked Joe in the glass room in the basement of the bookstore for days on end to teach him the value of books (which is definitely where Joe got the idea to imprison Benji and, later, Beck in that same place) and when Joe killed his first victim (the man his ex-girlfriend cheated on him with), Mooney consoled Joe by saying, "Some people deserve to die." The duo had a full-on Dexter style relationship, minus the ethical code that at least kept Dexter from murdering innocent people. (Technically, Beck can actually thank Mooney for her entire season 1 ordeal.)