'Mara' in Sanskrit. Anything that obstructs the attainment of liberation or enlightenment. There are four principal types of demon: the demon of the delusions, the demon of contaminated aggregates, the demon of uncontrolled death, and the Devaputra demons. Of these, only the last are actual sentient beings. The principal Devaputra demon is wrathful Ishvara, the highest of the desire realm gods, who inhabits Land of Controlling Emanations. Buddha is called a `Conqueror' because he or she has conquered all four types of demon. See Heart of Wisdom.