Dukkha

Dukkha was a manifestation of the Mara. He appeared to Tegan Jovanka in a dream. He tempted and tormented her with mind games and thought paradoxes until she agreed to a pact with him. The deal permitted the Mara to take her as a host, allowing it a physical presence in the real world. (TV: Kinda)

Behind the scenes
A concept of Buddhism is called which roughly translates to "suffering".