What is the essential difference between an ‘Ethical Hacker’ and a ‘Cracker’?

The ethical hacker uses the same techniques and skills as a cracker and the motive is to find the security breaches before a cracker does. There is nothing that says that a cracker does not get paid for the work he does, a ethical hacker has the owners authorization and will get paid even if he does not succeed to penetrate the target.