Well, Dr. Moreau from 'The Island of Doctor Moreau' is an evil doctor in fiction. He conducts cruel and unethical experiments on animals, trying to transform them into human - like creatures. Also, Dr. Doom from the Marvel Universe can be considered in a way. He is a brilliant scientist but uses his knowledge for evil purposes like world domination. Then there's Dr. Thredson from 'American Horror Story: Asylum'. He is a sadistic psychiatrist who pretends to be a good doctor but is actually very evil.
In fiction, Dr. Octopus from the 'Spider - Man' comics is an evil doctor. His mechanical arms that he fused with his body made him go on a rampage. He started as a scientist but his greed and ambition turned him into a villain. Dr. Strange (not the heroic one we know in the main universe) in some alternative storylines can be portrayed as evil. He uses his powerful magic for self - serving and malevolent ends. Also, Dr. Decker from 'RoboCop' is an evil scientist who has unethical plans regarding the creation of cyborgs.