Mara is anything that obstructs the practice of Dharma and seduces you into abandoning your practice for worldly activities. We tend to personify mara and think of it as an external being, like a demon, that torments us, but the four maras torment us far worse than any external demon ever could because it is these that have, throughout beginningless time, sent us again and again into the misery of the six realms. The first of the four maras is the deva putra mara, which is attachment to and craving for pleasure. The second, the klesha mara, causes one to take rebirth in the six realms of samsara. The third is called skandha mara because the skandhas or aggregates are the cause for the presence of suffering. The fourth one is the mara of death.