Villains who are Doctors (referred to as Mad Doctors), either medical or in some other fields such as psychiatry, robotics, physics and pharmacology. Often, they tend to overlap with Scientists (referred to as Mad Scientists), but not all Scientists are specifically Doctors and vice versa. Doctors mainly excel in various methods of healing and helping; Scientists mainly excel in the use of knowledge.

They are often obsessively involved in their studies to achieve whatever diabolical plans they have in mind, such as constructing an army to take over a region or the world or building machines to take control of valuable resources for their own purposes.