Malcolm Ramaker was a "entrepreneur" (Wynonna rephrases as "outlaw") in the 1860's, but was caught killing his business partner. Wyatt Earp sentenced him to hang where it took him 14 minutes to die.
Ramaker is first seen when Kiersten and Wynonna Earp get off the Bluntline bus headed to Purgatory. It's most likely that Ramaker is the one that caused the bus to get the flat tire. He kills and decapitates Kiersten and goes after Wynonna as well. She is able to defend herself and stab Ramaker in the eye before he runs off. Ramaker lures Wynonna to the Earp Homestead by kidnapping Waverly Earp and tying a noose around her neck. He reveals his plan of killing Curtis McCready to get Wynonna to come back to Purgatory and deliver Peacemaker. Wynonna is able to shoot the rope around Waverly, which ricochet off a pully and disarm Ramaker. Then, Wynonna shoot him with Peacemaker and send him back to hell.