The Janissaries were elite infantry units that formed the Ottoman Sultan's household troops, bodyguards and the first modern standing army in Europe.

They began as an elite corps of slaves made up of kidnapped young Christian boys who were converted to Islam as part of the devshirme and became famed for internal cohesion cemented by strict discipline and order. Unlike typical slaves, they were paid regular salaries. Forbidden to marry or engage in trade, their complete loyalty to the Sultan was expected. By the seventeenth century, due to a dramatic increase in the size of the Ottoman standing army, the corps' initially strict recruitment policy was relaxed. Civilians bought their way into it in order to benefit from the improved socioeconomic status it conferred upon them. Consequently, the corps gradually lost its military character, undergoing a process that has been described as 'civilization'.^[8] The corps was abolished by Sultan Mahmud II in 1826 in the Auspicious Incident in which 6,000 or more were executed

Edited from: https://en.wikipedia.org/wiki/Janissaries