Mind control is a favorite plot device in science fiction. It typically calls for a powerful manipulator to turn other people into drones using some extremely complicated-sounding, but often unexplained, process. It's a neutral power, used by heroes (Obi-Wan Kenobi) and villains (The Riddler) alike. Moral ambiguities aside, let's take a look at whether pop culture mind control could ever work in reality.
MYTH: Full Control of another Individual via Hypnosis
Not to pick on the Riddler in Batman Forever, as complete mind control is a common device used by any number of villains (particularly science-based ones) over the years, but I choose the Riddler as Jim Carrey jumping around in a green jumpsuit is permanently entrenched in my brain. The Riddler uses a device, the Box, to satiate its users to the point of becoming immobilized and at the same time drain their intelligence and memories.
Although the Riddler's motivations do not include control of the physical movements of his captives, let's include this as well. In order to control both the thoughts and movements of a group of people, remotely (and whether by hypnosis or some other means) one would have to gain access to entire portions of the collective brains and human physiology, as physical movement and long term memory are not controlled by the same region. This would call for a physiological change occurring at thousands of sites in multiple regions (motor neurons in the spinal cord, a reward system in the frontal lobe, control of precession movements in the cerebellum, etc.) in each and every person being controlled. Let's say this physiological change could be accomplished - even then, wide-scale mind control becomes a numbers game that's highly unlikely to work on a large number of individuals as shown in the movie. There are too many individual parts in to be manipulated to reach a desired result.
MYTH: Directed Control to cause a Single Desired Effect
Enough with the Riddler and my visions of Jim Carrey. You are more than likely familiar with the Jedi Mind Trick, which was first observed in Star Wars: A New Hope. Ben Kenobi, on Mos Eisley, waves his hands in front of some poor stormtrooper, and convinces the trooper that the droids in the back of the landspeeder, C-3PO and R2-D2, are not the ones that the Empire is currently scouring the desert planet of Tatooine to find. The trooper assuages, lets the land speeder pass, and probably gets shot later that night.
To cause an event wherein mental powers would elicit a desired and specific response (whether it be mental or physical) in another individual, say forgetting a previous command, would call for a disruption of the stormtrooper's working memory, and eliciting a desired response in the stormtrooper's short term memory long enough for the response to be vocalized and allow the group of desert scalawags to move along. This would be much more easily accomplished by misdirection, either verbal or physical.
However, if Ben Kenobi went to the storm trooper on Mos Eisley every day, for say, forty or fifty days and waived his hand and said, "These aren't the droids you are looking for," and then gave the storm trooper a star-cookie, this might work. He'd probably just be seen as creepy though. Which leads us too…
FACT: Influencing Behavior and Emotional Responses
As mentioned above, conditioning an individual over time, with either positive or negative reinforcement, could attain a desired response. This, went taken to a more extreme level calling for deprivation of the individual and lack of food, could break an individual's will and make the susceptible to influence or eliminate any response altogether. Both of these extremes of the scale, however, would take a phenomenal amount of time and action on the part of another party.
Annoying sounds (particularly bass heavy ones), odors, and use of light could get an emotional response quickly, one of confusion or disorientation, and are often used in control of large crowds.
One possibility that could work as well would be pharmaceuticals and other drugs. There has been a history of governments attempting to use chemical compounds to control the behavior of individuals, and we see it in practice in the medical community as well for the benefit of patients.
On this basis, one fictional character I would like to posit as being believable would be the Scarecrow, particularly as envisioned in Batman Begins. Using a mix of psychotropic drugs and imagery to cause hallucinations and induce fear and exploit the phobia of others – a destabilizing source along with reinforcement – would elicit an extreme emotional response, and if not gain a manner of control that would allow for the following of orders, obtain emotional domination over an individual. I admit I can't debunk this possibility – it would take some time to get the correct mix of pharmaceuticals, a method of administration, and specific environmental cues, but it might just work. Heck, the Scarecrow might be the most believable character to enter the realm of comic books who's not a guy in a trenchcoat with a gun.