A Loyalist refers to a wraith of the the Hierarchy that supported Charon, the Emperor of Stygia, during the Great War. In spite of his disappearance into the Onyx Tower with no explaination, those who were Loyalists believed that Charon and his style of rule were the best way for the Dark Kingdom of Iron to continue existing. They thought that the Smiling Lord, who had declared himself Emperor in lieu of Charon, would lead the Western Dead to ruin through his selfish ways and violent tendencies.
The Loyalists' biggest supporter came not from Charon, surprisingly, but from another Deathlord, the former Laughing Lady. Forced to abdicate the Seat of Succor and turn control of the Penitent Legion over to a puppet of the Smiling Lord, she managed to escape and spoke on behalf of those that wished Charon to continue his rule. Her presence as an "ordinary" wraith among the Loyalists inspired much support among them and for them until the Emperor's return.