Opposite from black hat hackers, these hackers hack to find flaws within a system (yes, they're hired all the time by major corporations to test their security systems) and disclose these flaws privately, allowing the company to patch up these flaws before black hats can take advantage of them. Here are some famous white hats:
Linus Torvalds is the creator of Linux, a family of operating systems that brought the flexibility and security of Unix-based systems to the public in an easy-to-digest manner.Started hacking by fiddling around with personal machines when he was a child. In 1991, he created the first version of the Linux kernel using the Minix operating system as his source of inspiration.
Tsutomu Shimomura is a white hat hacker who gets his fame from an incident with a black hat hacker, Kevin Mitnick. Specifically, Mitnick sent a personal attack to Shimomura by hacking into his computers. In response, Shimomura decided to help the FBI in capturing Mitnick.