The developer, or as it is abbreviated in Candy Box, DEV, not to be confused with the Devil, is the final boss of the game and appears in the level "Developper's computer". The developer, being over-powered, can kill you in seconds, no matter how much health you have (in normal gameplay, without randomized stats). The only way to kill him is to use an Invulnerability potion and hit all the keys on your keyboard as fast as you can and one of the keys will be the one to kill him. The key, however, is completely random. He has the same appearance as the Devil.
If the player cheats, however, and uses the Javascript/Developer's Console, they can set their health to NaN/NaN (thus effectively making them invincible) and fight the developper head-on, although his massive hitpoints make him take a very, very long time to kILL.