I hope it will come as no surprise to learn that serial killers get extremely unrealistic depictions in the movies. (They also are extremely over-represented. I once did some research and was able to estimate that there are approximately 10,000 fictional serial killers for every 1 real-world serial killer.)
In 2014, a team of ten psychiatrists led by Belgian psychiatry professor Samuel Leistedt set themselves a task: watch 400 movies about serial killers, and analyze which were the most and least realistic psychopaths. The team watched movies which were released from 1915 to 2010.
In real life, not all serial killers are psychopaths, and not all psychopaths are serial killers. In fact, most psychopaths (an estimated 1 in every 100 people is clinically psychopathic) never kill anyone. They simply manipulate, lie, and steal their way through life, living a life without remorse or empathy.
The team flagged 126 characters out of those 400 movies which they deemed legitimately psychopathic. Out of these, their top three most realistic were:
1. Anton Chigurh, "No Country For Old Men"
2. Hans Beckert, "M"
3. Henry Lee Lucas, "Henry: Portrait of a Serial Killer"
Their list of least realistic serial killers included:
1. Patrick Bateman, "American Psycho"
2. Hannibal Lecter, "Silence of the Lambs"
3. Norman Bates, "Psycho"