Gudon is an ancient Kaiju from eons long past and the predator of Twin Tail's species. Shortly after MAT discovered Twin Tail's egg, Gudon emerged from underground and attacked. MAT was quick to assault the whip-armed beast but the Kaiju was unfazed and retreated underground. The creature was recognized by a crew member as a long extinct creature Gudon. After doing some research, MAT soon discovered that the egg from before was that of Twin Tail, the instinctive rival of Gudon, which explained why Gudon had emerged.

After Twin Tail hatched and fought with Ultraman Jack, Gudon returned, confronting Jack and his archrival. His Color Timer had already started blinking and Jack ended up sandwiched between two bitter, ancient enemies. The two Kaiju were too much for Jack to handle, who had no choice but to retreat. With Jack out of the way, Twin Tail and Gudon collided and resumed their blood feud in a vicious fashion. The victor, however, was never revealed as the two Kaiju separated (inexplicably) for the time being.