Jack-O' Valentine (or just Jack-O' for short), is a character in the Guilty Gear series. She's one of the three Servants of That Man alongside Raven and I-No. Because her awakening remains incomplete, she can't function without her mask and toffee. Her past is shrouded in mystery, and her own memories are vague. Because she's in an unstable state, the tone of her voice changes rapidly.