Once Harry finally makes it into the Chamber of Secrets, the person controlling the giant basilisk isn't exactly who he was expecting. As it turns out, Tom Riddle, the intelligent teenager who everyone thought was responsible for ending the snake's reign of terror fifty years previously, was behind it all along. And what's more, he's Voldemort. Plot twist! Riddle's handsome but cruel, and is capable of a remarkable amount of menace for a 16-year-old memory ghost thing. The coolest part of this scene is when Harry finally manages to defeat him: in the book, he stabs the diary only after he's been cured by Fawkes, but in the movie, he does it with full knowledge that destroying Tom Riddle will likely be the last thing he'll ever do.