Near the beginning of the war, Dave and the plants were completely dominating with his newfound original agents of L.E.A.F (Repeater, Imitater, Explode-O-Nut and Meteor Flower), and Zomboss, though he would never admit it, was quaking in his boots when he saw that they would be arriving on Big Wave Beach (his base at the time). So much so that he decided to create the hulking abomination he called the “Gargantuar”, which was heavily mutated from the corpse of an asylum patient.

Due to this being the first-ever Gargantuar the agents of L.E.A.F were completely caught off-guard, causing two to die, one to survive heavily injured, and another missing afterwards but presumed dead. Though due to it being a prototype, this Gargantuar was incredibly unstable, causing it to rampage the area and Zombie property after decimating L.E.A.F, and the shock collar it was given only made it more angry, so much so to the point where it needed to be exterminated by Zomboss himself.

This led to the Gargantuar that’s known in the modern day, a bit weaker and less angry than the original and accompanied with a small imp to pilot it, but far less of a hassle for Zomboss to control.