how do celeb's choose a stagename?

[Radiospy]

hi
I am trying to find a website that tells you how many famous celebrities choose their stage name and why.
I can find plenty that tell me their original name etc.

anybody help?

[Metz]

Used Wikipedia for this..Elvis Costello ... Jake Riviera, suggested a name change, using Elvis Presley's first name and his maternal grandmother's maiden name to form Elvis Costello

[Memore]

when they register with equity they have to be the only one with that name if there is already someone with equity with same name they have to change it for example David Walliams is Williams but couldnt use same name as someone else in the union.