I designed the Game Genie!
Well, actually I joined Codemasters about six months after the original NES version was released, which in turn was about two years after it was designed (due to a long and very expensive legal battle with Nintendo), but I did most of the design and engineering work on the versions for other consoles.
I turned up as a freelance programmer/hardware designer/electronics hacker kinda guy, hoping to sell them a SEGA Genesis development system I'd made. They weren't interested (due to legal complexities) but they did ask me if I'd be interested in reverse engineering the Game Boy and designing a Game Genie for it.
Too right I was! So, I set up in a rather rickety Portakabin (they'd run out of office space) with a logic analyser, a special screwdriver (ever noticed how the Game Boy uses special 3-slot screws?), an FPGA programming system, a large amount of soldering irons, wires, chips, etc, and an especially loud stereo system.
About three months later (imagine some kind of mad scientist, banging and clattering into the night in a shed at the bottom of the garden - not far off), there was a hardware prototype that worked, and a rough spec of how to program the Gameboy.
A nearby console development company were contracted to do the software while I finished off the hardware and migrated it to an ASIC (i.e. prepared the prototype chip design for mass production). The ASIC design got sent to a Korean chip fab, who, two months and about $100,000 later, sent back a batch of 48 chips (known as 'engineering samples') for testing... Oooh, I was so chuffed! They even had 'LoftLogic' written on the top, just like I'd asked! (Well, they contained Logic, and by this time we'd moved into a Loft above a garage at Codemasters, so there y'go; LoftLogic!)
Anyway, it's a very long story, and involves over the next year or three the development of the SNES, SEGA Genesis, Game Gear, SEGA Master System Genies, as well as the far superior Genie II for the SNES/Genesis (which sadly never made it to market... I've got one of only 5 SNES Game Genie IIs in existance in my cupboard)...
Aaah. They were happy days...