Big Daddy was apparently a gas attendant before the undead apocalypse. During the outbreak, Big Daddy died and reanimated.
For years, Big Daddy lurked at the gas station, searching for any nearby cars to fill with gas. When Riley Denbo and Cholo DeMora scavenge the neighbourhood for supplies, they use fireworks to hypnotize all the zombies, except Big Daddy. Big Daddy tries to snap his fellow zombies out of the trance, but fails.
Later, when the humans begin gunning down any zombies in their way, Big Daddy tries to get some zombies out of the weapons' way, but couldn't save much. In a fit of grief and rage over his fellow zombies' deaths, Big Daddy attacks the leaving humans, and manages to grab one's AUG. Big Daddy and an army of his fellow zombies, including Number 9 and the Zombie Butcher, and the zombiefied Blades and they march towards the Pittsburgh Outpost with Fiddler's Green, a place where the priviliged people of the outpost reside, as a primary target, to take revenge on the living for all the suffering they have caused the zombies.
When the army arrives at a blocked pathway, Big Daddy gets the Zombie Butcher to use his meat cleaver to break through the wall. Big Daddy looks through the opening to see several fellow zombies hung up as target practice, further fuelling Big Daddy's rage and grief.
Overwhelming the military post the "Throat", Big Daddy and his army reach the river surrounding Fiddler's Green. When Big Daddy realizes that he and the zombies cannot drown as they are already dead, they march across the river bed and into the city on the other side of the river.
Big Daddy and his army rampage through the streets of Pittsburgh towards Fiddler's Green, killing and/or devouring any living humans in their way. The army reaches Fiddler's Green, and Big Daddy and the zombies use blunt objects they acquired earlier to break into the mall and slaughter the upper-class snobs.
Big Daddy encounters Paul Kaufman, and when the latter shoots the former, an enraged Big Daddy attacks and follows Kaufman into the garage. As Kaufman's servant abandons him, Big Daddy notices and recognizes a fuel pump near Kaufman's limo. Big Daddy then fills the limo with gas and leaves a trail up to the garage exit. At the exit, as Kaufman is attacked by a zombified Cholo by his limo, Big Daddy kicks a lit blowtorch towards the limo, igniting the gas and killing Kaufman.
With a large number of the city's residents slaughtered and their revenge taken, Big Daddy and his army leave the city in search of somewhere they belong.
Big Daddy was highly intelligent compared to most other zombies. He also felt empathy for his fellow zombies, even killing those who were suffering and anger and hatred towards the living for the pain and suffering they were causing the undead.
While a smart zombie, Big Daddy often has lapses when confronted by things that remind him of his past life. Which in turn often make him reenact moments from them. At his Gas station, even when there are no humans present, he finds himself habitually trying to fill the nearest cars with gas as though he was still working there. When he confronts Kaufman, he stops briefly when he sees a gas pump and haphazardly plays around with it, before using it against the limo.
Big Daddy is often prone to pained screams whenever a situation angers/saddens him or whenever he realizes the life he had can never be taken back.