When X5-494 had been a kid – back when he was just 494 and the world made more sense (or, really a lot less sense but, y'know, brainwashing)- names weren't something they had. They had designations because they were solders.
Only people had names. The doctors, the nurses, the guards. Lydecker.
Not X5-494. Not the others. Not a single X.
Then they get sent on missions. They were given cover names.
John Hammonds. William Faust. Simon Lehane.
They made sure X5-494 understood that they were not his names. He used them, dropped them, and at the end of the day returned to Manticore. He was a soldier, to be used and discarded as his superiors saw fit.
(And he never questioned it. Not until Rachel. He never fully stopped after that)
And then he met 452 – Max. Max who said everyone needed a name, and she didn't mean the doctors and nurses and guards and Lydecker and Ordinaries. She meant them – Manticore's soldiers and creations.
She named him Alec.
And it was strange. It wasn't a cover name to be abandoned when the mission was over. It was his name.
Alec kind of liked it.