Apollyon was made from the soul of a servant who had killed his master to take over his household and gain al that he had. apollyon had become a level one akuma. so he went across the country of north america for a short time. he then evolved to level 1.5. he still has no free will or thought of his own, and simply continues to due what is in his nature. after a little while, he evolved to level 2. he still had very little free will, but still was able to comprehend the most basic of ideas. after a couple of years, he comes across a general. naturally, the generals first instinct was to kill the akuma. the general and the akuma fought, but the akuma quickly began to become overwhealmed. it seemed as though the battle was all but lost until a freak accident happened.
A massive tremor came across the entire country. this caused the general to trip and fall down from the unexpected happening. at that very moment a sudden sense of self worth came over the akuma and in a great fit of rage, it began to barrage the fallen general with nothing but slashes to the body. as the general took his last breathes, he said, "why..why do you attack me..why do you let the noah control you like a dog?..tch, your nothing but an apollyon..a tool, made for destruction.." and he died. even though he had no capacity for rational thought, something had seem to get through to the akuma. "apollyon..". this word would become the akumas name he had given himself, moments before he transformed into a level 3 . after becoming a level 3, apollyon continued killing, and doing whatever the noah had told him.
Although now he had grown a personality, and a thinking mind. with each task assigned to him, apollyon began to question his masters. he began to wonder, why he had to follow their orders. why he had to follow without question or comment. in his mind he began to build a great dissdain and hatred for the noah and all other beings which hindered akuma. he grew an ambition. one day, apollyon was sent on a suicide mission with two other level 3's to kill allen walker and destroy the entire black order. the noah knew that three level 3's could never pull this off, but since they were disposable, they would make a good decoy.
The other two akuma were ready to blindly carry out the mission, but apollyon had questioned the order. when he did this, one of the noah threatened to make him self destruct. apollyon still resisted but then a noah began to commence the sequence and apollyon knew they were serious. so the three akuma headed off to the black order headquarters in north america. the trio managed to cause some destruction and kill a couple of generals, but they were outmatched. so the 3 merged together to form a giant akuma. the giant was brought down by some generals and left in a feild for dead.
Many days later, the carcas began to move, and apollyon reborn ripped out of its stomagch. he is now a level 4 akuma. his mind is open and his power surpasses the noah themselves. now he plans and calculates, pushing to fufill his secret ambition...