Donald's father had experienced a worsening of his mental stability for a number of years. One night Wendell snapped; he got into a barroom argument where he shot and killed the bartender. Returning home, Wendell then proceeded to kill his three oldest children. Sally managed to flee the house with five-year-old Donald; intent upon killing them as well, Wendell kept firing until his cheap gun exploded and disfigured his face. Finally Sheriff Greeley arrived on the scene, shooting and killing Wendell when he refused to stand down.
How much of young Donald's resulting mental illness stems from this early trauma, and how much of it was hereditary via his father, is not known. But within a year or two Donald had "started lighting fires in people's trashcans and running away", eventually giving him a nickname for life. Shortly afterwards Sheriff Greeley married Sally, which only caused Donald's pyromania to escalate.
Finally at age of 11, Donald set fire to an abandoned house which burned to the ground. Despite Sally's threat that she would divorce him (which she promptly made good upon), Greeley had Donald institutionalized at a facility in Terre Haute, where he remained for two years.
Due to extensive electroshock-therapy treatments, Donald suffered permanent damage to his memory and cognitive abilities, and was an academic failure upon returning to school. At 16, he dropped out and went to work at a car-wash, where he was subjected to jeering, taunts and physical abuse by the residents of Powtanville. Within a year he snapped again and set fire to the local Methodist church.
Now an arsonist with a criminal record, Donald was sent to juvenile detention and, when he turned eighteen, adult jail. Strangely, despite dealing with hardened inmates and nightly unpleasantries such as prison rape, Donald found life on the inside preferable to that in Powtanville. He became a prison "trusty" by the time of the superflu outbreak, and was sent to care for dying prisoners in the infirmary. Once the entire staff and population of the prison were dead, Donald simply wandered free and went home.
Donald has fantasized for years about setting the tanks at the Powtanville oil-depot on fire; now, there is no one left to stop him from igniting everything and anything he wishes. He begins his transformation into the completely insane "Trashcan Man" persona, torching first the tanks at Powtanville, then the town of Gary, Indiana, suffering permanent injuries in both incidents.
Trash is receptive to the call of Randall Flagg — who seems to have taken a particular interest in him, above nearly all other potential followers. Trash begins to worship Flagg; "my life for you" becomes his mantra and battle-cry, as he heads west to Las Vegas, Nevada. In Trash's imagination, Flagg's city is a glittering desert paradise called "Cibola" (the reference is to an old conquistador legend.)
The journey west is fraught with hardship for Trash, both physical and mental. Southwest of Sterling, Colorado he has a particularly terrifying and dangerous encounter with a diminutive sociopath from Louisiana called The Kid — who initially seems jovial and friendly. As they are both heading to Las Vegas, he even gives Trash a ride in his tricked-out deuce coupe.
But The Kid turns out to be quick-tempered, temperamental, emotional, violent, and gun-happy. He endangers Trash's life with his reckless driving, directly threatens him with bodily harm and death on repeated occasions, plies him with alcohol at gunpoint, and even sexually assaults him. But worse: The Kid brags about his intentions to enter Las Vegas, feign his way into Flagg's good graces and then overthrow him. To the Trashcan Man's ears this is intolerable blasphemy; but Flagg reassures him in a dream that he has the situation under control.
One evening in the Rockies, while The Kid and Trash are navigating the blocked roads, Flagg summons a pack of timberwolves. The Kid leaps for the protection of a derelict car, which some of the wolves encircle. A grim vigil begins; either hunger, thirst, or daytime heat will finish The Kid off, or else he will grow desperate and try to fight his way through the ring of wolves.
The remaining wolves of the pack lead Trash safely through the Eisenhower Tunnel, going under the Continental Divide and passing the Rocky Mountains. From there he can safely complete his westward journey alone.
Trash makes it through the desert — horribly sunburned, dehydrated, and in terrible physical shape, having literally walked the shoes off his feet — and finally reaches Las Vegas. He leaps into the fountain at the MGM Grand Hotel, before crawling inside the casino and passing out on a gaming table.
The Trashcan Man is introduced to Lloyd Henreid, and shortly afterward Whitney Horgan, Ace High and Heck Drogan. He is welcomed into the Las Vegas community by Flagg's special orders, and initially put to work wrapping copper wire at Hoover Dam. Having never belonged anywhere before, Trash is deliriously happy to have a productive new life, surrounded by friendly people.
That very day he comes to know the dark side of living under Flagg's rule, when Heck is caught freebasing cocaine and Lloyd must enlist Trash's aid in his public crucifixion. Lloyd belatedly offers Trash one of Flagg's special tokens: a black stone with a red flaw, identical to the stone Lloyd wears. Trash accepts the charm without question and dispassionately assists in nailing Heck to the cross, realizing that this is the price for his new life.
Later in the evening Lloyd summons Trash to meet Flagg, who receives him warmly with the reassurance that "his dreams are true dreams", and a promise that he will "set him to burn."
The Trashcan Man turns out to be a mechanical savant, with a gift for working with incendiaries and explosives. He also reveals a sixth sense for finding such materials and devices where they might be scattered in the desert, hidden at various abandoned military installations. His skills become crucial to Flagg's plans for launching an airstrike upon the Boulder Free Zone by spring.
However, Trash is still insane and prone to psychotic breaks. On one occasion his fellow workers begin teasing him about his pyromaniacal tendencies; it triggers in Trash a violent flashback to being surrounded by the jeering tormentors of his youth in Powtanville. Trash snaps. Covertly he begins to sabotage all of the fuel-trucks and helicopters at the Indian Springs airfield. There are two detonations on two separate days, damaging valuable equipment — and more importantly, killing all of Flagg's pilots.
Wandering in the desert, the Trashcan Man recovers enough of his wits to realize he has erred colossally in judgment; failing his dark master, his life is forfeit. He considers immolating himself, but decides suicide would be insufficient penance, and that he must atone for his mistake by bringing Flagg some truly tremendous gift out of the desert. At an Air Force range northwest of Indian Springs, Trash discovers a nuclear warhead. Managing with difficulty to winch it up to ground level, he attaches it to his sandcrawler and begins to drive back to Las Vegas. He arrives downtown with his payload, just as Larry Underwood and Ralph Brentner are scheduled for imminent public execution by dismemberment.
Having neglected to use any special protection in handling the warhead, the Trashcan Man is in the final, gruesome stages of radiation sickness. Lloyd Henreid demands to know what Trash thinks he is doing, and orders him to take the bomb away, while Flagg whines impotently behind him, terrified.
The "hand of God" detonates the weapon, destroying Las Vegas and vaporizing everyone at ground zero, "righteous and unrighteous alike."