"User X", would somebody please 'explain me'?!

A long time ago in a debate forum far, far away, a person that was debating suddenly turned into "User X"...now I see this happening more and more frequently (but with different users).

Could somebody please explain to me how someone goes about changing their CZ identity to "User X"...I figger if any/every one can do it, I have a boatload of old posts I'm not so proud of, and I should get on this bandwagon, too!

Blessings -

Unyquity