d. Thought Police
Orwell was born on June 25, 1903.
1984 is such a huge landmark in literature, many of the concepts it introduced have entered the common vernacular. In addition to the Thought Police, the book's evil overlord "Big Brother" has come to symbolize any totalitarian dictator.
And the author himself lent his name to the adjective "Orwellian" which is used to describe institutionalized oppression.