The title was misleading. I assumed a "Web App Hacker" was someone who creates web apps, not someone who breaks into web apps ("Web App Cracker"). AFAIK, hacker news is not a news site for people who break into web apps.
Dafydd Stuttard (book author) / PortSwigger created the Burp Suite web application security testing program, which I've found invaluable in performing security analysis of web apps during development.
Kevin Mitnick was not a cracker, he was a hacker.
Hacking has multiple definitions.
Hacker is a word with many valid definitions.