A developer is somebody who has made a game and has uploaded it to Kongregate. A developer is marked with a next to their names in chat, and on their profile. Some of the more famous developers on Kongregate include:
jmtb02: Developer of such greats as the Dark Cut, Four Second, and Ball Revamped series.
preecep: Made the largest flash game in history: Desktop Tower Defense, which Kongregate was lucky to sponsor, but unfortunately has not done anything else.
Eggy: Made the Draw-Play series, among a few others.
DrNeroCF: Made The Fancy Pants Adventures, which was the very first game to recieve a card. Kong also exclusively recieved The Fancy Pants Adventures: World 2 Demo, and gave a badge to Nuclear Eagle.
Jiggmin: Made both Platform and Kongregate Racing, two of the first, and still most popular, multiplayer games on Kong.
Dreygoth: made very crappy games and is the noob developer god of kongregate