Believe it for not, Cyber's real name is actually Percy. Cyber got his nickname due to being Project Cybernetic Matrix, Cyber for short. He dislikes his actual name through, so he goes by his project name "Cyber". If anyone finds out about his real name he'll say it's actually Percival. It is unknown whether that is true or not.

His full official name is,

"Cyber" Percy/Percival Jackson Robotnik.

Bonus:
Metal chose the middle name, Cyber sometimes hates Metal for that and calls him Zeus sometimes due to his ability to control Lightning and because "they're both big, but important, jerks."