The Gorkanaut is a large, heavily armed walker created by the Mekboyz and piloted into battle by a lone Nob. Much larger than a Deff Dred, it is essentially a small Stompa. It sports a myriad of heavy weapons, including twin-linked big shootas, a deffstorm mega-shoota, twin rokkit launchers, a skorcha and a suped-up power klaw. The Gorkanaut is a brutal engine of destruction that serves as a living avatar of Gork upon the battlefield.
The Gorkanaut is pretty well armored with 13/13/12 and 5 hp (pre-8th edition). The Deffstorm mega shoota, which pumps out a whopping 3d6 s6 ap4 shots a turn can turn an entire tide of GEQ's into a fine meaty paste. This loadout is very nice on the overwatch, with lots of dakka being supported by a template. Also is s10 ap1 with 4 attacks and rampage in CC, so it'll shred most things it comes into contact with. Overall, it's an infantry wrecker. Has a 6-Ork transport capacity with no assault vehicle or firing points for...reasons, so don't use it to transport anything that wants to assault or shoot.
A tactic that is sometimes used is to have at least three Gorkanauts that will become huge fire magnets not only because of their standard meganess, but because they get additional rules as the game goes on. On Turn 2, they get Rage, On Turn 3, they get Hatred, and after that, they get Shred. Let them survive that long, and you'll have the ability to crush anything you get near.
The Gorkanaut's brother is, of course, the Morkanaut.