How does one become a hacker? A true hacker , I mean pure hacker.

As with all things IT, there is both a formal path or a DIY path, and it depends on what your end goal is.

Hacking is a very broad church, and not how the movies portray it hitting the "hack" button on a keyboard. Social engineering is always on the increase and is as much a part of hacking as computer based attacks on systems. Penetration testing is also another area that can fall under the hacking umbrella.

Legal hacking as a profession within IT security can actually pay really well depending on your skill set, and some places will require you to have formal qualifications, such as Department of Defence (or MOD for the UK) or Federal police agencies, and a number of universities in the US and UK offer short and long qualifications (usually under titles like "Ethical Hacking" or "Applied Cyber Security"). There are also a number of certifications in security, like Comptia.

On the informal side and hacking for a hobby, there's a lot of really good book and websites on cyber security and hacking (securi has some really detailed information of hacks and security breaches), and I'd recommend anything by Kevin Mitnick (for social engineering), and it's both informative and entertaining. There may also be meetup groups in your area that practice ethical hacking, which is a good place to ask advice and get a start.

And then its persistence, practice and application.