Roland Deschain is born to Steven Deschain, ruler of the Barony of Gilead in Mid-World. He is trained in the ways of the gunslinger, an ancient order that uses their skills to defend justice and right. After his father loses his throne, Roland sets out on a quest to the Dark Tower. He begins this quest an isolated loner, cold-blooded in his pursuit of the objective. As he proceeds and forms a ka-tet with Jake, Eddie, and Susannah, Roland comes to value human connections and love, which prepares him to successfully complete the quest.
Born John Chambers to a TV executive and his wife in New York and raised by his nanny, the boy who joins Roland on his quest goes by Jake. He appears in The Gunslinger when he comes to Mid-World for the first time after being hit by a car. When Roland lets Jake die, he must draw Jake back from New York and bring him into the ka-tet that is his destiny. Jake learns the ways of the gunslinger and becomes as adept at fighting as any other member of the ka-tet.
Roland pulls Eddie Dean out of a drug-induced haze in 1987 New York. He helps Eddie escape his dealers and brings him to Mid-World, promising him a life of purpose and adventure. Through his quest Eddie finds love with Susannah, but he also discovers all the terrible things he thought he knew about himself were wrong. He discovers his own intelligence, talent, and courage through the quest.
Susannah Dean begins her life as Odetta Holmes. After Jack Mort drops a brick on her head when she is a child, she develops a split personality with a second persona, Detta Walker. Detta allows her to express all the anger she can't express as Odetta. Roland fuses Odetta and Detta into Susannah when he shows her Jack Mort being hit by a train—the same train that took her legs when Jack Mort pushed her in front of it. She navigates Mid-World in her wheelchair and endures a sexual encounter with a demon, a pregnancy shared with another woman's body, and the deaths of two people she loves. Yet Susannah believes in the quest and follows Roland for as long as he needs her.
Father Donald Callahan
Father Callahan's disgrace as a priest results from him jumping from a window in America to escape vampires. He lands in Mid-World and establishes a ministry in the Calla, giving help and comfort to the people of the harsh farming region. When the ka-tet comes to the Calla and saves the town's children, Callahan leaves with them, hoping to fight evil once again. He later sacrifices himself to save Jake and Oy from a bar full of vampires and cannibal mutants.
Mordred is the biological child of Roland and Susannah, the result of two separate encounters with a dual-gendered demon. He is the spiritual child of the Crimson King and Mia, which makes him dangerous to the ka-tet. He lives less than a year, only growing to adolescence, but he is able to shift from human to spider form from birth. His first meal is his mother Mia.
Roland first knows Walter O'Dim, born Walter Padick, as one of his father's ministers, unaware that Walter also inhabits the persona of Marten Broadcloak, Steven Deschain's sorcerer who seduces Roland's mother. The highest lieutenant of the Crimson King, Walter appears in many worlds under many names. He is the man in black Roland pursues across the desert, and is also known as Richard Fannin, Randall Flagg, the Covenant Man, and the Walkin' Dude.
The Crimson King was once a real king, though his name is never given. He is a powerful force of evil with magical powers. He is the man behind Sombra Corporation and North Central Positronics, and he works tirelessly to destroy the Dark Tower. Once the Dark Tower is destroyed the Crimson King is promised dominion to remake existence and rule over it as he wishes.
Stephen King becomes a pivotal character in his own series once the ka-tet learns of his existence, when Father Callahan discovers he is the subject of one of King's books. Roland and Eddie visit King and learn he is only a conduit through which ka tells the story of the Dark Tower, but he is also helpful, dropping items and messages into the narrative to assist the ka-tet. Jake dies saving King from a runaway van in 1999 so King can finish the story.
Oy's past before he meets the ka-tet is a mystery, but he follows Jake, Eddie, Susannah, and Roland with unparalleled loyalty. He provides comfort to Jake, who remains a boy even though he becomes an accomplished gunslinger. He also attacks the giant were-spider Mordred when Mordred attacks Roland, and dies defending his master.