The Reaper

God of Death is the world's best assassin.

Later it's revealed that he is not real God of Death, real master assassin knows as "God of Death" is Koro-sensei

Appearance
Contradictory to his name, God of Death has a somewhat innocent looking and friendly smile. In his disguise, he has short hair and is always seen with his cap. Without it, he has a skull face without any skin, due to him ripping it off.

Personality
As the world's best assassin, God of Death is a sadistic person, saying terrifying things such as dividing Irina Jelavic into pieces and drowning Korosensei with the entire Class 3-E students without the sligtest hesitation.

History
God of Death was born in an extremely wealthy family. One night, his father was killed by an assassin. God of Death saw the assassination act from a window and he admired the assassination, calling it "A beautiful skill". Thus motivating him to become an assassin.

Plot
He is first mentioned by Lovro when Nagisa asks about the world's best assassin. He appeared to Class 3-E in the disguise of a florist in order to sell them some flowers, which they would later give to Karasuma to give to Irina Jelavic. He had planted a bug in the flowers to gain Intel on Irina before moving in to kidnap her. After Korosensei left for Brazil, he took the opportunity where there were no teachers available to approach the students. He showed them a picture of Irina in captivity and said that if they didn't rescue her he would dismember her and then send her back to school piece by piece. This was also where he displayed his inhuman powers, such as natural blending in with the classroom to appear invisible and disappearing silently and without a trace after throwing some petals in the air.

Abilities and Powers
At first glance he doesn't seem to be very wicked, but this is one of his best skills and assets, the power to appear as a harmless individual, when in fact he is more dangerous than the so called un-killable Korosensei. Upon his first appearance, he appeared before Lovro undetected and had him comatose with ease. He is singularily responsible for the decrease in assassins lately and defeated them all by himself. He is so powerful that rumours persist that he is actually ten people as opposed to a single one, and instances in the manga imply him to be almost supernatural in power.

One skill unique to him is his control of his bloodlust, either hiding it completely along with his presence making it appear like he is "blending" into the background or releasing so much of it that it actually becomes a sort of "shroud of darkness" that makes it even impossible to see his body, and instead all that can be perceived in an oncoming shadowman.

He has shown himself a powerful and intellectual planner, trapping the entire Class E and even Korosensei into his trap with ease and any miscalculation was nothing he could not handle and take control of. His planning is aided by his use of technology in place of accomplices to preform multi-person tasks with only himself to operate. He was seen using a remote to operate certain contraptions around his entrapped hostages, and control doors and bars.

Deceptively, he is an extremely powerful hand-to-hand combatant, a trait unusal amongst assassins at it is useless in the field 99% of the time. However the other 1% of the time, it is fundamental should an assassin ever find himself in such a fight. As such The God of Death developed his skill in this area to such an extent that he could defeat almost every member of Class E that specialized in hand-to-hand combat, including Nagisa.

Another of his powerful skills is his marksmanship. He uses this skill to attack targets at a long distance and while in motion to the extent of successfully shooting someone through the head in a bypassing train. His shot was so precise that he completely hit all of Korosensei's tentacles as he tried to grab hold of the floor. despite their intense speed, also showing impressive eye-sight, and with this skill alone he overwhelmed and trapped Korosensei.

Trivia

 * His technique of becoming a shadow-like being to commit assassinations is similar to some accounts of death where people report shadow people encroaching towards them as they die.
 * Instances in the manga resemble him as either as flower, a skull or simply a shadow.
 * When described by Lovro, the image used in the manga resembled a man holding a book.

Quotes

 * (To Class E students) "It's impossible for humans to reap the God of Death. Do not fear, there is only the God of Death reaping man."