Manhiel was an egotistical, vicious, almost demonic entity whose powers were strengthened by the suffering around him. He claims to be the cause of all the evil in the galaxy and is the known ruler of Deroth having shaped the world in his image. He is perhaps the most well-known villain of The T.A.'s stories.
Manhiel is summed up in one word Evil he cares for no one, and will stop at nothing to get what he wants, best described by Eurybus as a little child who didn't get what he wanted. Manhiel however is someone you do not want to underestimate, he is capable of godly feats, and how far he is willing to use them is beyond what any mortal could expect, going so far as to flay Alatariel "Elmora" Tamriel again, and again for disobedience.
Manhiel has no redeeming qualities, he has no emotions, and finds pleasure in tortuing others, he has spent hundreds, if not thousands of years abusing Elora Tamriel, for his own sexual pleasure, but besides the fact that he is a monster he is also the puppeteer behind The Battle of Deroth, which resulted in him gaining more power over the Valinus brothers, thus showing that he is a genius.
Manhiel died mortal, and regretted his sick, evil actions, showing that to some extent that he was capable of emotion, but the development of this was left in ruins after he died from his wounds.
Not much is known about Manhiel, it is speculated that he is either a God, or Demon, as he refers to lesser beings as mortals, but his true origin is left shrouded in mystery.
Manhiel didn't make an appearance, until after The Outlaw was revealed to be Ramasus Ei Valinus. Manhiel took his time to explain stating that he had been following the T.A. For quite some time, and enjoyed their little adventures manipulating it to his own cause (e.g. Keeping them alive) he also resurrected Elora before The Battle of Deroth.
He took Ramasus's form, and tricked The Learner, and Elmora, and attempted to kill the both of them, but it turned out that the Learner had known, and had allowed Deroth to possess him once again, becoming the Darklord. The 2 fought it out for some time, but were evenly matched, and eventually they both had to give up.
The ruion Spike Dimentos was able to make Manhiel mortal, with a special weapon the wounds were made worse by Ramasus who charged at Manhiel effectively throwing the two of a balcony Manhiel who was dying begged Eurybus Valinus to end his suffering, but Eurybus ignored the pleads.
Manhiel spent a good few minutes coughing on his own blood, during which time his memories began to swarm him now mortal, he felt the pain that he inflicted on other people, dying human he silently whimpered that he hoped the T.A. Would forgive him.
His decaying body would eventually wash away.
The Dark Being version of himself was helpful against evil, which probably was part of a plan to get close to the alliance. In the end, he escaped after hitting Spike, finally to grow back to Manhiel. In the end, The Writer and The Beginner killed him.