Three Big Things:
1. Responsible for the best-known and arguably most influential set of legal codes in the ancient world. Key issue: they were written down and publicly posted.
2. Brought Mesopotamia together as a more-or-less united empire (this time with Babylon as the seat of central authority) for the first time since Sargon six centuries prior.
3. Seriously, the written law thing. It’s just huge. “An eye for an eye”? That was his. Innocent until proven guilty? Also his, although not phrased quite so smoothly. A chance for the accused to defend themselves? Punishment fitting the crime? Throwing people in rivers to see if they float? That’s Hammurabi, baby.