A more specific pen name question

[siebendach]

OK, suppose I write thrillers. (I don't, but suppose). My name is Casper Milquetoast and I want to use the pen name Brock Samson.

"Casper Milquetoast" owns the copyright, because Brock Samson's not a real person. (Or, if he is, he's someone I've never met and had nothing to do with writing hte book.) The cover art says "Brock Samson".

What about the ISBN? Is the ISBN attached to "Race to Midnight, by Brock Samson" ? Or "Race to Midnight, by Casper Milquetoast" ?