Jon Lech Johansen (and his blog)
DeCSS (background article only, at Wikipedia)
Also since the beginning, DVDs have had the option of embedding a region code in the DVD disc. Different regions of the world were assigned different codes, and every DVD player manufacturer had to sign an agreement with the DVD Consortium stating that they would only play DVD discs of a certain region. And the manufacturers had to play by the Consortium's rules, because the Consortium was the only one who could give out the decryption keys that would allow the player to decrypt the CSS encryption used on commercial DVDs.
DVD region codes
Eventually the multi-region DVD players got so smart that they were software-indistinguishable from region-locked players, and the studios gave up and focused on a new threat: DVD ripping programs. As I mentioned earlier, DVDs contain executable code that tells the player what to do next-go to this menu, set this register, jump to this track or chapter, etc.
Macrovision introduced yet another protection scheme called RipGuard. They reverse-engineered several DVD ripping programs and created a protection scheme that exploited as-yet-unknown bugs in those programs. They also claim to be able to "update" the protection for new discs as bugs are fixed in the ripper programs.