A father of lies
The Mockinglord was a mighty spirit and an enemy of the Arbiter. He tried to turn Justiciar Gyleon against the Arbiter, only to realise too late that Gyleon had remained loyal, leading to the Mockinglord's defeat and imprisonment in the Sanctum centuries before the events of the Battle of Shatterbridge. Though he was imprisoned, his agents continued to do their work, amongst them the Smiling Man.
He was freed upon the death of the Arbiter.
Danton Redwind made a pact with him, binding him to Danton for all intents and purposes. This allowed the Mockinglord to get close to Radiance during the Eclipse, and did not stop him from making a deal with Pietro Gori, in which the runes necessary for Binding Radiance were given to him. The cost, as it turned out, was the Republic being invaded by Malvern. Though the Mockinglord beat Danton's consciousness into submission, the fate of the two is as of yet unknown.