The Wraiths are elemental beings originally from the Argent D'Nur dimension until it was absorbed by Hell. They were deified and feared by the original people of the Argent D'Nur and protected by the finest warrior order of the dimension, the Night Sentinels as a means to harness their tremendous power as a energy source and defensive measure against hell.
During the war, they gave the Sentinels necessary power to defend the realm from Hell's legions. However, a Hell Priest by the name Deag Grav and his cabal used the Wraiths' essence against Argent D'Nur with the help of a traitorous Night Sentinel by forming the Well, which enabled Hell's forces to gain an upper hand and finally claim victory over the realm. After Argent D'Nur was absorbed into Hell, their souls were trapped in the Hell energy sphere until the Doom Slayer used the Crucible to free them.