At some point in the late 1800's Jonas was killed by Wyatt Earp and was resurrected as a revenant.
Through flashbacks, Wynonna reveals that she slept with Jonas in order to cope with being almost killed by Jack of Knives and finally killing The Seven. When they meet again in Everybody Knows, Jonas shows himself to be a revenant and Wynonna reveals she's pregnant. Jonas is excited about being the father, hoping that the hybrid child will be the "start of a new race" and that he'll be famous among the revenants. Even though he might be the father of her child, Wynonna can't let the other revenants know that she's pregnant, so she sends Jonas back to hell with Peacemaker.
Relationship: one night stand