Stefan Esser, better known in the jailbreak community as i0n1c, was responsible for one of the most successful exploits in jailbreak history. While the iOS 4.3.1 jailbreak was certainly a collaborative effort, Esser's work was perhaps the most important.
No one likes to connect their iDevice to their computer every time they reboot, and i0n1c's untether meant they didn't have to. What made it so successful? The fact that the exploit continued to work through iOS 4.3.2 and 4.3.3 updates.
Have you ever wondered what goes into hacking the most secure mobile operating system? Esser tells all in this 97 page paper...