Farmer Brown was a microbiologist turned supervillain.
Farmer Brown was a microbiologist and agriculturalist who had developed a way to cause massive growth in animals, which he tried to market as a way to end world hunger. However, during a public exhibition of a giant sheep, it grew irritated, escaped from its cage and attacked the crowd.
Though the sheep was subdued and captured easily enough, Farmer Brown was arrested. At his trial, Enoch Brown was found guilty of reckless endangerment and was ordered by the courts to cease all experiments and remove all his already existing giant animals from Gotham.
Brown protested that his intentions were noble and that he invested years of work and his entire savings in this project, and this injunction will ruin him. The judge retorted that Brown ought to have considered controlling his animals prior to the debut, and the decision stands. Disgruntled, Brown resolved to himself that "they will see some real monsters".
Sometime later, Farmer Brown released a swarm of giant preying mantises out onto the streets of Gotham. Batman was instantly on the scene. The mantises proved to be too much for Batman, but without explanation their bodies disintegrated. It was later revealed that Brown had genetically engineering the insects to have a short lifespan, and the forthcoming fight that would end rather quickly was a warning to show what Brown was truly capable of.
Afterwards, Farmer Brown released a number of grotesquely mutated farm animals including a bull and a cow, and a flock of mutated chickens. Though Batman, Robin, and Batgirl managed to stop the animals, Farmer Brown had made his point and demanded fifty million dollars or he'd release his mutated insects again, this time leaving them without the genetic defect.
Commissioner Gordon seemed to comply and had Harvey Bullock take in the money, but when Harvey was discovered to have followed Brown's daughter, Emmylou, to his "farm", and that the money was fake, Brown decided to release the bugs. Bullock was thrown to a giant mutated pig, and Farmer Brown and Emmylou faced off against the heroes. Though Bullock was saved, Emmylou had been granted superhuman strength from using beef steroids and managed to beat Robin and Batgirl.
Brown himself fought Batman with an electrified pitchfork, but only succeeded in subduing him by using Robin and Batgirl as ransom. With the bat family defeated, Farmer Brown put them into a rocket along with several giant bug cocoons and sent them flying towards Gotham. However, Batman managed to escape, release his sidekicks and destroy the rocket along with the bugs before it reached the city. Farmer Brown and Emmylou were then taken into police custody.
In the DVD commentary of "Critters", Glen Murakami and James Tucker reflected in hindsight that rather than using the never-before-seen Doctor Moon, they would have better brought back Farmer Brown to replace Hugo Strange in Justice League Unlimited once the Bat-embargo vetoed any further appearances of Strange in the show.