Long answer (Quoted From the Robot Chicken Wiki FAQ):
As editor of ToyFare Magazine, Matthew Senreich had struck up a correspondence with Seth Green. Green, it turned out, was an avid action figure collector and fan of the magazine. The two hit it off due to their mutual interests. Later, due for an appearance on Late Night with Conan O'Brien, Green came up with the idea for a stop-motion action/adventure segment featuring toys modeled after himself and Conan O'Brien. he called Senreich and asked for his involvement. While the two worked on the Conan project, a Sony website caught wind of the idea and approached the two about creating an Internet-only series based on the concept. In 2001, Sweet J Presents launched on Screenblast.com. Suddenly with a wealth of stop-motion animation experience, Green and Senreich pitched a concept to Mike Lazzo & Adult Swim and Robot Chicken was born. I mean, hatched.