Klephts (Greek κλέφτης, kléftis, pl. κλέφτες, kléftes, which means "thief" and perhaps originally meant just "brigand") were highwaymen turned self-appointed armatoloi, anti-Ottoman insurgents, and warlike mountain-folk who lived in the countryside when Greece was a part of the Ottoman Empire. They were the descendants of Greeks who retreated into the mountains during the 15th century in order to avoid Ottoman rule. They carried on a continuous war against Ottoman rule and remained active as brigands until the 19th century.
The terms kleptomania and are derived from the same Greek root, κλέπτειν (kléptein), "to steal".
After the Fall of Constantinople in 1453 and then the fall of Mistra in the Despotate of the Morea, most of the plains of present-day Greece fell entirely into the hands of the Ottoman Empire. The only territories that did not fall under Ottoman rule were the mountain ranges (populated by Greeks and inaccessible to the Ottoman Turks), as well as a handful of islands and coastal possessions under the control of Venice. This situation lasted until at least 1821, although there were some parts of Greece, such as Macedonia and Epirus, that still remained in Turkish hands until the 20th century. This period of time in Greece is known as the Τουρκοκρατία or "Turkocracy."
Ottoman lands were divided up into pashaliks, also called eyalets; in the case of the lands that form present-day Greece, these were Morea and Roumelia. Pashaliks were further sub-divided into sanjaks which were often divided into feudal chifliks (Turkish çiftlik (farm), Greek τσιφλίκι tsifliki). Any surviving Greek troops, whether regular Byzantine forces, local militia, or mercenaries had either to join the Ottoman army as janissaries, serve in the private army of a local Ottoman notable, or fend for themselves. Many Greeks wishing to preserve their Greek identity, Orthodox Christian religion, and independence chose the difficult but liberated life of a bandit. These bandit groups soon found their ranks swelled with impoverished and/or adventurous peasants, societal outcasts, and escaped criminals.