Megabyte

"Mainframe will burn and Megaframe shall rise out of its ashes!" - his catchphrase Megabyte is an evil virus from the Mainframe and the arch-enemy of Enzo Matrix guardian of the Mainframe. When he heard that Enzo had gone to the world Lyoko on a mission, he planned to go there and have revenge against him.

About
Megabyte also has the ability to attach and detach his legs whenever he is sitting in his throne. He also can extend deadly claws from both his knuckles and fingernails. He has a pet null called Nibbles whom he referred to as his father. But was later revealed to be a nullified sprite of Welman Matrix who was Dot and Enzo's father.

Megabyte was known all over Mainframe for his reputable fights with his sister, Hexadecimal. The pair were created when the virus Gigabyte was caught in an explosion, and each got specific attributes: Hexadecimal got strong, chaotic power. Megabyte got brawn and a calculating thought-process.

In Roleplay sessions
Megabye attacked Enzo and Derek when they were training in the Desert Sector of Lyoko. Both Enzo and Derek couldn't beat him and were beaten up badly and Derek was killed. Then eventually, Derek returned to the world of Lyoko to save Enzo and defeat Megabyte. When he was hit by the full force of Derek and Enzo's energy blasts, he exploded and was killed instantly.

X.A.N.A. resurrected Megabyte's body and possessed it so it could use it as a body to fight Enzo and Derek. Megabyte was defeated once again but this time he had been controlled by X.A.N.A. so he wasn't his real self. He is currently deceased.