Samuel was a skilled and ruthless assassin before meeting his end, manifesting in Hell in the form of an anthropomorphic black cat which served as a reflection of his soul based on his life and sins. At one point your late mother came into contact with him, begging for him to take care of you and keep you safe. For one reason or another he promised to do so, and due to being a demon he became contractually bound to his agreement.

He has been in service to you as your guardian and butler ever since.