Dufus P. Ratchet was born with a malfunctioning pituitary gland that allowed his body to continue to grow to monstrous proportions, while his mind stopped developing past the intelligence of an 8 year old. The simple minded Ratchet was kept under observation at Central City's Breedmore Mental Hodpital.
Major story Arcs
When several members of Flash's rogues gallery conspired to destroy the scarlet speedster ( Barry Allen) they freed Ratchet from his cell and outfitted him with high- tech armor provided by the Monitor. Using an elaborate deception, the villains made Ratchet think that Flash had beaten them up and even kiled a small rodent. Incensed that a super hero could kill a defenseless creature, one of the few friends Ratchet thought he had, he went on a rampage, trying to kill the Flash. Finally subdued, Ratchet was taken by the Flash to Gorilla City where their super-science corrected his mental deficiencies. Ratchet became a near IQ genius and is now a respected member of society.
Justice League International
Sadly the hightened IQ was only temperary, and sometime later Big Sir joined the Injustice League. Big Sir has been a member of The Justice League Antarctica group which consisted of his fellow Injustice League members. G'Nort, a Green Lantern was also a short time member. Their sole JLA adventure involved destroying flesh-eating penguins, an incident which demolished their headquarters. G'Nort's ring kept them alive until rescue came.
Big Sir and the rest of the InJustice League members were sent on a solo Suicide Squad mission. Big Sir died from a close explosion from a small robotic looking child.
Big Sir's first appearance is on The Flash episode "The Elongated Knight Rises." He is played by former pro wrestler Bill Goldberg. Big Sir doesn't appear to have any metahuman powers; he's just a very strong criminal. He's not mentally impaired, either.