Mara is Buddhism's personification of everything that keeps beings bound to suffering and rebirth, desire, death, and delusion given a face. His defining appearance comes at the decisive moment of the tradition: as Siddhartha Gautama sits beneath the Bodhi tree on the verge of awakening, Mara assaults him to prevent it, first with armies of terrifying demons, then with his three seductive daughters (Craving, Aversion, and Passion), and finally with the challenge that the seeker has no right or witness to his enlightenment. The Buddha's response is the celebrated gesture of touching the earth (bhumisparsha mudra), calling the earth itself to bear witness to the merit of his countless lives, and the earth quakes in assent, and Mara is dispelled.
Beyond that scene Mara recurs throughout the early texts, appearing to tempt or discourage the Buddha and his disciples, and his name is used as a category: the tradition speaks of the "four maras", the mara of the defilements, of the aggregates, of death, and this personal deity, so that Mara is at once a mythic being and a name for the forces within the mind that resist liberation. He is the Buddhist adversary, not of a creator God, but of awakening itself.