Thought Police are a largely fictional concept connected to the New World Order and dystopian fantasy as well as numerous conspiracy theories - in general they are seen as a type of "secret police" who will enforce the will of autocratic overlords via censoring, intimidating and even abducting those that dare to question the will of authority by expressing political or social opinions not favored by the elite (and often deeply corrupt) officials.
The Thought Police may employ many techniques to abolish free-will, such as mind-control or brainwashing but they can also simply work within the confines of "red tape" and propaganda so as to imprison those they view as a threat or even engineer society itself so that the "masses" turn against "free thinkers" and thus put immense pressure on the "deviant" to join the rest of society or face becoming a social pariah / outcast.
Media Dealing with Thought Police
Parallels With Reality
like many urban legends, conspiracy theories and dystopian fiction the Thought Police do have parallels in reality, a great many dictatorships employed secret police to enforce their will and some continue this practice well into the modern era : this coupled with fear and distrust of authority even in democratic nations often leads to exaggerated accounts of mind-control experiments, mass spying, "Big Brother" tactics and even accounts that all major atrocities and wars are orchestrated by elite and hidden societies intent on global domination.
Due to the fact some of history's darkest regimes (Nazi Germany and Stalinist Russia) heavily employed secret police the concept has become imprinted into the social psyche as a strong and near-instinctual fear of a return to fascist or autocratic ideals on a global scale.
The idea also has some ancient roots, since the Christian Bible made a prophecy that the Beast would force many evils upon mankind during the End Times, such as forcing society to worship it and wear its sign : the symbolism is seen by some as a warning of a global fascist state that will act as a spiritual opponent to free will (seen by Christianity as a divine gift).
Big Brother (popularized the idea of fascist overlords in the public mind as well the ideas many associate with dystopian fantasy) Men in Black (a specific type of "thought police" popularized via UFO folklore and believed to intimidate and silence any who have knowledge on alien craft or entities)
New World Order (a secret society believed by fringe societies to either have achieved or seek global domination - sometimes viewed as a spiritual entity akin to the Biblical Beast, other times is simply viewed as an elite society of humans.. UFO folklore often ties them with a larger Alien Invasion scenario)