A.J. Crowley and
Aleister Crowley are one and the same. In
Good Omens, at least.
Despite Crowley's answerphone message of
"Hi. This is Anthony Crowley. Uh. I...", The relationship is strongly hinted at in one of the footnotes:
"He'd slept right through most of the nineteenth century, for example. Not because he needed to, simply because he enjoyed it.*
* Although he did have to get up in 1832 to go to the lavatory"
Given the huge line of aliases
Aziraphale has taken, it's pretty reasonable to assume that
Crawly has done the same.