Dukkha

Dukkha was a manifestation of the Mara.

Biography
Dukkha 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 allowed the Mara to take her as a host, allowing it a physical presence in the real world. (DW: Kinda)

Behind the scenes

 * A concept of Buddhism is called Dukkha.