Sephiroth was born in Nibel Mountain Reactor. He was produced by Professor Gast. He was the one that was created in Shinra`s procejt to create an Ancient. Shinra took him to the army, an he became a high-respected officer in SOLDIER.

Then, one rainy day he and a an named Zack from SOLDIER travelled to Nibelheim along with two militaries. One of them was Cloud. When they came to Nibelheim to take away all the monsters that was disturbing the Reactor, they had to cross a bridge. The bridge broke, and Sephiroth, Cloud, Zack, Tifa and the other military fell down. One of them was never founded again. Sephiroth, Zack, Cloud and Tifa continued to the Reactor. When they reached it, Zack and Sephiroth went inside. In there, they found out about Shinra`s monster project, as one of the tanks opened and a monster escaped. Sephiroth started to wonder, and they all headed to Nibelheim. There Sephiroth locked himself up in the Shinra Mansion basement, were he started to read. He read as if he were posessed, and then , one day, he changed. Zack went down in the basement to check him. Sephiroth had discouvered the thruth about himself. He allso discouvered that Jenova still was alive. She lived inside Nibel Mountain Reactor. He told Zack that he was a traitor, that his ancestors had let the Cetra down, and that was why the Cetra was dead. Zack tried to stop him, but then Sephiroth said:
"Out of my way. Im going to see my mother."

Then he burned Nibelheim down. He killed the inhabitans, and then he headed towards the Reactor. There, he killed Tifa`s father. As Zack entered the Reactor, Tifa had tried to kill Sephiroth, only to be almost killed herself.
Zack challanged Sephiroth, and got beaten. Then, Cloud came. He helped Tifa, and as he headed into the room were Sephiroth and Jenova were, Zack asked him "Kill him for me, wont you?" Cloud too challanged Sephiroth, and got beaten. But then, as Sephiroth walked out of the reactor, Cloud charged again. Sephiroth took his sword and stuck it into Cloud`s chest. Cloud managed to lift Sephiroth with the sword, and Sephiroth falled in the Mako pool. Shinra papers announced him as dead. But that was a lie. Weither Shinra knewed that Sephiroth was alive or not is still unknowned. But, one day, Sephiroth attacked the Shinra Building. He realesed Jenova, which Shinra had transported to Midgar after Sephiroths "death". Then Sephiroth faced President Shinra, and killed him.
He got chased by Cloud and the others, and when they after a long chase reached Ancient Temple, he were there too. He explainded how he would find the Promised Land and destroy the planet. Then he got Cloud to almost kill Aeris in an atempt to get the Black Materia that Cloud had taken from Ancient Temple.
After that, Aeris disapeard. Cloud and the others tracked her to the old Ancient City. When they after a big ruckus found her, Sephiroth came from nowere and killed her. Then he ran away, as Cloud and the others fought Jenova L*I*F*E.

Sephiroth ran to the Norhtern Continent, were he got followed by Cloud`s party. When they had reached the Crater, Shinra employe Heidegger and Scarlet came, in Highwind. Sephiroth fouled Cloud so Cloud gave the Black Materia to him. Then Sephiroth again tried to foul Cloud and get him to believe that he too was created by Shinra, that Cloud was a bad copy of Sephiroth. Then, Weapons awoke and came out to crush the humans.
Sephiroth created a barrier around Northern Crater to protect himslef and Jenova.
He allso used the Black Materia to summon Comet. Cloud disappeared and got flushed right through the earth, flowing inside the Lifestream.
When Shinra defeated Diamond Weapon, they used the Sister Ray to blow it down. After they had loaded the cannon with Mako energi from the 8 reactors, leading all power to Sistery Ray and put whole Midgar in darkness, they blowed a hole right through Diamond Weapon. This was after that Cloud and his friends had stopped it from attacking Midgar when the canon was still being loaded. The blast from Sister Ray continued after hitting the Weapon, and it succeded in hitting the barrier, and destroy it.
Cloud and his friends climbed all the way down to him, were they challanged him. After first defeating Jenova`s final form, they met with Sephiroth. He turned into a bizzare creature, but got beaten. Then, he turned into SAFER Sephiroth, also knowned as the One Winged Angel.

But, Cloud and his friends beated even this creature, an with pain, SAFER Sephiroth turned into small small pieces and vanished. As Cloud and his friends thought that it was over, they remembered the Comet. Then, suddenly, something happened to Cloud. His mind was transported to a strange place, and as he flew through magical tunnels, he saw Sephiroth.

Then, in a duell between Sephiroth and Cloud, Cloud let loose all his anger on Sephiroth. With the limit combo Omnislash, he slashed Sephiroth more then 9 times. Then, in a big jump with his sword raised over his head, he executed Sephiroth. Sephiroth stared at him, his face was covered with blood. Then, he again turned into small small pieces. He became a part of the Lifestream. Sephiroth was dead.