The Double, novel by Fyodor Dostoyevsky, published in 1846 in Russian as Dvoynik. It is a classic of doppelgänger literature.
The Double is the first of many works by Dostoyevsky to reveal his fascination with psychological doubles. The morbidly sensitive and pretentious clerk Golyadkin, already clinically deranged by the social pressures of his office and by unrequited love, suffers a growing persecution mania, which leads him to encounter another man looking exactly like him who is the leader of a conspiracy against him. He is finally driven to a madhouse by a series of encounters with this being, who is sometimes clearly his own reflection in a glass, sometimes the embodiment of his own aggressive fantasies, sometimes an unpleasant ordinary mortal who happens to have the same name and appearance, and sometimes, in some supernatural way, himself.