Abused since childhood by a sadistic stepfather, Billy Milligan "went to sleep" and created twenty-three other personalities to cope with the abuse. Many of the personalities expressed extraordinary talents for languages, medicine, or painting, while others were petty criminals and thieves whose crimes got the others into constant brushes with the law. Still others were children incapable of dealing with adult life.
To control the chaos, three of the dominant personalities—Arthur, Ragen, and Allen—took over the major tasks, assigning each of the other personalities goals and duties based on their individual talents. Personalities who did not contribute or who were seen as threats to the stability of the whole were declared "undesirable" and banished from holding the consciousness.
- William Stanley Milligan: The original, unfused personality. Started life as a shy but brilliant boy who was gradually driven to suicide by abuse. The dominant personalities prevented him from killing himself and instead "put him to sleep." As the original personality, Billy can never be declared undesirable, but the others rarely allow him to regain consciousness.
- Arthur: An aloof intellectual who studies science and medicine, he controls who gets to "take the spot" (i.e., which personality gets to assume consciousness).
- Ragen Vadascovinich: The Yugoslavian bodyguard who provides physical protection for the group, particularly for the children. Has Super Strength and controls the spot while Billy is in jail. He takes his name from the phrase "rage again".
- Allen: A fast-talking Con Man responsible for concealing the group's existence by creating explanations for whatever weird situations they find themselves in and smoothing away incongruities in their stories.
- Tommy: A teen with a gift for machines and technology, Tommy is allowed to use his criminal talents (such as picking locks, dismantling doorknobs, and shedding straitjackets) to insure that the others will never be held against their will.
- Danny: A fearful little boy who Does Not Like Men after being Buried Alive by Billy's step-father. One of his few pleasures is his talent for drawing and painting.
- David: Another child personality, his role in the "family" is to deflect physical and emotional pain from the others by absorbing it himself.
- Christene: A sweet, pretty, assertive little girl. As a young child, Billy consciously created her as an imaginary friend, only to have her take on a life of her own during his abuse. As she was the first personality to be created, the others have forbidden that Christene should ever be made Undesirable. Instead, they take pains to protect her and to insure her behavior is safe and appropriate.
- Christopher: Christene's older brother, he appears to be a mere counterpart to his sister and rarely takes part in the action, though it's known that he enjoys music and plays the harmonica.
- Adalana: A melancholic lesbian who craves love and affection, she is the only personality with the ability to "wish" control away from Arthur so that she can assume the consciousness whenever she likes—a fact of which the other personalities are not aware.
- Philip: A small-time thug with a strong Brooklyn accent, he had a talent for coming up with criminal schemes, which he and Kevin would then carry out.
- Kevin: Another small-time criminal, though less intelligent and motivated than Philip.
- Walter: An Australian who fancied himself a big game hunter, he was banished for borrowing a gun (for the safety of Billy and the children, only Ragen is allowed to handle weapons) and shooting a crow (an unnecessary death that distressed the children).
- April: The bitch. Arthur was originally charmed by her intelligence, but he quickly learned that her only motivation was to kill Billy's stepfather and deemed her dangerous to the group.
- Samuel: The only religious personality, he identified strongly with Billy's Jewish biological father, who committed suicide when Billy was young. Banished due to his judgemental self-righteousness, he is allowed to assume consciousness on Yom Kippur, so that he can fast and atone on the off-chance that the body has a soul.
- Mark: Referred to by the others as "the workhorse," Mark handled monotonous labour for hours without complaint, but otherwise had no initiative of his own, listlessly awaiting further instructions. Arthur deemed Mark's willingness to accept and follow orders a risk to the group.
- Steve: An egomaniac who thought himself superior to others, he refused to acknowledge Billy's existence and insisted he was the real main personality and the others were merely his alters. Arrogant and condescending, he was banished for exposing the group to danger in prison, where his attitude was not appreciated by the guards and other inmates.
- Lee: A cruel, vicious practical joker with no respect for any authority, Lee couldn't keep his mouth shut around other inmates—or prison guards—resulting in his banishing.
- Jason: The pressure valve, Jason screams, rages, and throws tantrums to let off steam. His rage was deemed inappropriate to the group.
- Robert: A daydreamer who talked of his grand plans for self-improvement. In reality, he was too lazy to move beyond them to action. Arthur banished him for contributing nothing to the group.
- Shawn: A deaf child, Shawn was presumed by the others to be mentally challenged and removed from consciousness for his (and their) safety.
- Martin: A snob and a braggart who put on airs and pretended to be a genius and a social climber in order to impress others. Banished for threatening Arthur's authority.
- Timothy: A child personality who, like many of the other children, was subjected to sexual abuse at the hands of Billy's stepfather. When a man made a sexual advance toward him, Timothy was so terrified that he voluntarily withdrew from the Real World.
The system slowly spiraled out of control, finally shattering when "Billy" was arrested for the abduction and rape of three women. Adalana, a lesbian personality, claimed responsibility for the rapes. In a landmark decision, Milligan was found not guilty by reason of insanity, the first and only time DID has ever been determined as a mitigating factor in a felony case. Originally sentenced to a mental institution, legal arguments broke out as to whether he deserved prison for his crimes. Meanwhile, doctors frantically worked to fuse his personalities. During therapy, another personality, the Teacher, emerged as a fused "potential" of all the other personalities with uninterrupted memory. With the Teacher's insight, doctors were temporarily successful in integrating all the personalities, but when Milligan was finally moved to prison, the fusing broke apart, with the personality Ragen stepping forward to protect the children for a final time.
Milligan& served his prison sentence and was released in 1988. Ragen appears to have dominated the decision against integration, unable to believe that it would mean anything other than the "death" of the child personalities, and the group remained a collective. Legal and financial issues caused them to move to Japan, where they and Keyes published a sequel,The Milligan Wars. The Milligan Wars has not yet been released in the United States due to "Son of Sam" laws that prevent convicted felons from profiting from selling the rights to their stories. Milligan& eventually returned to the States, where Milligan died of cancer in 2014.
A screenplay titled A Crowded Room, based on The Minds of Billy Milligan, has been in the works since the 1990s, with such names as James Cameron, Joel Schumacher, and Leonardo DiCaprio attached, but has remained in Development Hell due to rights issues.
- Abusive Parents: Chalmer is a particularly horrifying example.
- American Accents: Philip has a Brooklyn accent, and April has a Boston accent.
- Bedlam House: What happens to the inside of Billy's brain when Arthur loses control of the Undesirables.
- Berserk Button: Anybody who dares try to hurt Christene will feel Ragen's wrath.
- Bruiser with a Soft Center: Ragen robs, deals drugs, and threatens to break bones—but put a child in front of him and he's pudding. The other selves are aware of this and use the knowledge to defuse him before he hurts himself, especially by trotting out Christene. Even Christene herself manipulates Ragan of her own initiative to stop him from "doing bad things."
- Cheerful Child: Christene seems to have been created specifically to be a non-neurotic, lovable child who can interact with the world without the trauma of the abuse shared by the others.
- Depraved Homosexual: After being sexually abused by Billy's stepfather, the group tends to react toward all homosexuals as if they are predators.
- When Timothy's homosexual boss makes a friendly pass at him, Timothy is so terrified that he retreats inward and never interacts with the outer world again.
- David encounters a drag queen in a public restroom. David's confusion and terror causes Ragen to come forward. Assuming that David was threatened, Ragen beats the drag queen senseless. Then when Ragen leaves, Phil and Kevin step in to steal the drag queen's wallet without the knowledge of the others. This inspires them to a short-lived crime spree targeting homosexual men (who, in rural Ohio in the 1970s, would be unlikely to go to the police).
- Does Not Know His Own Strength: Ragan. More correctly, he can't understand that not all the other personalities possess his strength, even though they're all in the same body: on Christene's first day of school, she tries to pick an apple for her teacher, only to be frustrated when she can't reach the one she wants. Ragan appears, tears down the entire branch, and gives it to her. When Ragan vanishes, Christene is deprived of her super-strength and drops the branch in the road, where it is squashed by a car.
- Escape Artist: Tommy's talent is encouraged by Arthur, who purchases different kinds of handcuffs and locks specifically so that Tommy can take them apart and figure out their weak points in order that no one in "the family" will ever be held against their will again. While in police custody, Tommy removes his straitjacket. When the police ask him how he did it (explaining that it's normally used for people who might otherwise harm themselves), he shows them the trick, then teaches them how to put one on so that no one can escape from it.
- The Face: Allen generally does all the talking for the "family", due to his fast-talking and sharp mind.
- Feminine Women Can Cook: After Billy, who previously enjoyed helping his mother in the kitchen, was beaten for "acting like a girl" and "doing woman's work," he developed the personality of soft-spoken, shy Adalana, for whom "woman's work" was appropriate. When Billy is an adult, Adalana is the one tapped to do all the cooking for the group.
- Freudian Trio:
- I Just Want to Be Loved: Adalana uses this as an excuse for raping three women
- Jerkass: Many of the Undesirables are Jerkasses, particularly Philip and Kevin. In the case of Martin and Steve, it appears they were declared Undesirable specifically because they showed no traits other than being Jerkasses.
- Jerk with a Heart of Gold: Tommy, who, while being antisocial, unsympathetic and hot-headed, seems to genuinely care for the child personalities. In contrast to many other personalities who were made Undesirable for far lesser offenses than Tommy, Tommy remains part of the group solely because he uses his criminal talents only to protect the group.
- Justified Criminal: Ragen commits robberies, sells drugs, and becomes involved in low-level organized crime in order to feed the "children," who are crying with hunger. He also breaks into a medical supply warehouse in order to steal a wheelchair and leg-braces for an impoverished child.
- Just Like Robin Hood: Ragen. Though a hardened criminal, he has a strict code of honor: he will not rob or harm a woman, and he will do nothing to hurt a child. His ethics rule him out as a suspect when the others try to determine which personality committed the rapes.
- The Mean Brit: Arthur has a tendency to be this, due to the necessity of remaining in absolutely control of a chaotic situation. He doesn't give second chances, which is why there are more Undesirables than active personalities.
- Morality Pet: Christene, for Ragen.
- My Nayme Is: Christene spells her own name with an e. The others spell it the usual way: "Christine."
- Nice Job Breaking It, Hero!: All the personalities are guilty of this during their "mix-up times," but Ragen is especially prone to doing this, and Adalana finally gets everyone arrested because of it.
- Papa Wolf: Ragen
- Quintessential British Gentleman: Arthur. At one point he runs away to England, buys a bowler hat and an umbrella, and proceeds to horrify the native-born Englishmen.
- Real Person Cameo: Dr. Cornelia Wilbur, who treated Sybil, is called upon to formally diagnose Milligan after his arrest. (In Real Life, after the publication of Sybil, Wilbur made a living as an expert on multiple personality disorder.)
- Revenge Against Men: April seems to have been created to deal with Billy's murderous rage against his stepfather Chalmer.
- Revenge Before Reason: April again. She is described as a psychotic capable of filling the other personalities with intrusive thoughts of torturing and murdering their stepfather. At one point, she almost seems to possess Ragen, whispering in his ear constantly. She convinces Ragen to go as far as driving to Chalmer's farm with a sniper rifle and hiding in the woods near his house before Arthur realizes what has happened and declares her Undesirable.
- The Spock: Arthur. Billy even compares him to Mr. Spock specifically.
- What the Hell, Hero?: A lot of the personalities make questionable decisions.
- Adalana and all of her damn raping
- Ragen's sterling morality regarding women and children falls flat when you consider he's a drug dealer whose product is probably ruining more than a few women and children's lives.
- A psychologist chides Ragen for calling himself "the protector of children" while allowing poor David to feel the pain for the entire group. Ragen, flustered, feels guilty enough to allow the psychologist access to the group's child personalities.
- Phil and Kevin are opportunistic criminals who take advantage of the lack of protection for homosexuals in order to rob them and beat them with impunity.
- Arthur (who up to this point has been the voice of reason) blows the family's savings in order to visit his "homeland" of England. His trip forces Ragen to return to crime in order to pay the bills, which gives Adalana the opportunity to take advantage of his amphetamine-induced fugues so that she can emerge and rape women, which in turn ultimately leads to Billy's discovery and arrest.