In the final days of the Deroth Wars, Satan released the devourer demon, Hellfire, as a last resort to wipe out everything. Ramasus and the Writer were helpless to watch as Hellfire began to devour the demonic dimension, soon to move on and devour everything. Hellfire was a kind of organic Reality Bomb, born to kill everything, and the only thing that could stop him was if a demonic being - a cruel, emotionless monster - willingly gave it's life to stop him.
The Learner shed his Dark Lord persona, and gave his life to kill Hellfire.
Because of his unselfish act, the entire dimension began to collapse. The T.A. members escaped without harm, but the Learner was lost in the dimension-wide collapse. So were all Demonata. But something happened. Some kind of external force - maybe the Pantheon of Discord, maybe Manhiel, maybe plain bad luck - caused Deroth to combine itself and all it's occupants into a single being. The being, calling each-other Deroth after their home, joined together. A billion, billion Demonatic souls, and the souls of a thousand Dark Gods, as well as 1 Timelord, combined themselves into a horrific, twisted, unimaginably powerful Dark God.
Attack on the T.A.
Deciding to avenge their death, Deroth became obsessed with destroying the T.A. The first attack was on the main building, when they killed a group of guards at the the Academy on New Gallifrey. Soon afterwards, Ramasus Ei Valinus was attacked while driving on a motorway. The car he was driving was ripped in half and Deroth very nearly killed him, before going into deepspace to regrow their strength. And this was only the beginning.
Behind the scenes, Deroth joined the dark brotherhood known as The Darkness, under the command of Darkness. Sent on a mission to exterminate Manhiel in any way possible, Deroth took their chance when the Learner came to him. The Learner sensed that Manhiel was possessing Ramasus, so he needed to be powerful when he attacked. Deroth jumped at the chance, and they took their old host back. Using all of the power they had, Deroth's soul mesh combined themselves into a single being, finally transforming into a more powerful, singular being.
Deroth attacked Manhiel, intent on destroying him.
Because of external forces, Deroth ended the battle and attempted negotiations before leaving. Darkness informed Deroth that Manhiel would come to devour him, and as part of the stratagem, Manhiel had to believe that Deroth was dead. Landing on a planet and killing all the inhabitants, Deroth allowed Manhiel to devour his body, but his soul mesh escaped. Keeping his part of a bargain that he and Darkness had made some time before, Deroth gave the Learner to Darkness in exchange for another body. This Deroth was much weaker, but still cunning and dangerous. Deroth is currently serving Darkness in this state.