Sinis was a Shade who served under the Deceiver.
During the Great War, the Deceiver had a clash with the Watcher on one point, possibly during the battle for Tyr, and Sinis was thought to have died when Mazzarin collapsed the the Shrine of Nyx upon him.
This was proven false as when the Five Champions rescued Alric from the Deceiver's captivity in the Barrier and Sinis showed up with an entourage of Myrmidons and Soulless to deny them escape. After a brief exchanging of words, his force was destroyed after Alric unleashed several Dispersal Dreams. Sinis was then killed for good after a duel with Alric.