Where to start?
To unlock the first iPhone he created the first Jailbreak.
He did BlackRa1n - JailBreak and
BlackSn0w - unlock
All current Jailbreaks use the LimeRa1n exploit - discovered by young Mr. Hotz because SHAtter had been pre-announced so he decided to beat them to it.
He was an original member of the Dev Team before they fell out over release timings.
He also discovered the 5.8 Bootloader bug among other things.
He was arrogant and an attention seaker and also the only person I have ever talked to who made me feel like I really was nowhere near his level of intelligence. Others may know a lot more about their subject than me but I can hold my own in a conversation with them. He was just a genius.