Cleo Dahmer is a semi reoccurring character in Liam's stories, who serves as an antagonist of some form in every incarnation.
Most of Cleo Dahmer's past is unknown. However what is known is that she is the head of all research on the Left Hand parasites. She worked closely alongside the director in his search to weaponize the parasites, and managed to learn an incredible amount of information about them in only a few years. After the director's death, she took over the entirety of the organization and changed their goal from weaponizing Left Hands, to pure study of them.
She presumably works for the same organization, but is studying the Styx Hound instead of the Left Hands. Whether or not both exist in the same universe is unknown. After John's grandfather stole and hid the infant Styx Hound, Dahmer spent years searching for it, and then almost just as long searching for a way to recapture it. She ultimately decided to liberate two of the creature's vessels and use them to retrieve its one weakness. The contents of a canister kept in the same building it had taken over.
In each of her incarnations Dr. Dahmer's personality is that of a scientist in the purest sense. She looks upon the unknown in wonder and awe, while looking upon that which she has discovered with pride and contentment, She takes no greater joy than that which is found in learning and researching something new, often spending Anywhere between weeks and months running constant experiments without pause. Unfortunately for those around her though, she is only interested in her research, and holds no regard for morals or ethics in her experiments. Inflicting test subjects with varying diseases, injuries, and even torture, simply for the sake of seeing what will happen. The only thing that matches her cruelty is her egocentric pride. Her belief that she can plan for any contingency, that she often underestimates those around her. For example allowing the Styx hound to escape because she did not believe it had the mental capacity to solve puzzles.
Cleo Dahmer has no extraordinary abilities, physical or supernatural.
Cleo Dahmer bears a peerless degree of knowledge and intellect, understanding complex concepts such as matter distortion, reanimation, and interdimensional travel with little to no difficulty, and in some cases, even educating others in these concepts. She is capable of planning out plots and schemes years in advance with almost no room for error.