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 permitted the Mara to take her as a host, allowing it a physical presence in the real world. (TV: Kinda)

Behind the scenes

 * In Buddhism, one of the is  which roughly translates to "suffering."
 * As well as its Buddhist meaning, Dukkha's name is also a play on the word "Doctor".