Alastor is an archdemon, and the chief executioner in the monarch of Hell. One of his epithets is the "Evil Genius of the Household" meaning that Alastor is the demon that conducts the most heinous, depraved, and unbearably cruel tortures in the pits of Hell.
In times, Alastor was associated with both Greek and Roman mythology. In Greek mythology, Alastor is associated with the sins that pass down generations from fathers to sons. In the Roman mythology, he is notorious as the evil genius of the household who entices residents to commit sins. He is often associated with family feuds.
Out of all the demons in the infernal Pit, Alastor is arguably the most cruel devil of all, even for a demon, especially in his sadism. His only rival being the King of Hell himself, Satan. The more pain he could deliver the happier he was, but not just physical pain; he was also effective in mental torture and stress. He viewed torture as an exquisite art and enjoyed being patient and relishing the moments where he tortured his victims.
Almost all of the demons that roam Hell fear Alastor greatly, almost as much as they fear the Lords of Hell themselves. It is because of this that he was handpicked by Satan himself, due to being impressed by his skills, as the Grand Torturer of Hell. Alastor has even gathered and formed his own group known as the Malebranche; a group of demons comprised of twelve elite fiends that share Alastor's taste in sadistic torment.