On the road to Lud, Jake finds a wounded "billy-bumbler". These animals are described as looking like a cross between a raccoon and a dog, with a corkscrew-spiral tail. Introduced in The Waste Lands, the third book in the series, Oy befriends one of the main characters, Jake Chambers. When Jake first sees the bumbler, he calls "Come here, boy," and the animal mimics the sound with "Oy". The bumbler is friendly and intelligent -- Roland explains that it used to be common for billy-bumblers to speak and even be able to perform simple math -- and Jake decides to call him Oy, after the first word they heard him say. Seemingly a mere pet at first, Oy proves to be strangely helpful in times of need and nearly human at times in both intelligence, and compassion.

At the time of their meeting, Roland concedes that Oy may quite possibly be meant as another member of their ka-tet. Later, in the 6th book, this is confirmed when the Tet Corporation forms as the association of "Deschain, Dean, Dean, Chambers, and Oy."

Oy develops emotions and even a sense of humanity past that of his ability to replicate some words that the others speak. Oy is often referenced as the smartest bumbler that people have seen since the world had moved on. Oy, much like Jake, shows times when he's able to retain his original instinct and innocence that he had before the quest while playing with Jake or during times of rest for the gunslingers. During the quest or when a problem comes up Oy is a valuable ally.

Oy finally dies in the last Dark Tower book. He saves Roland's life by attacking Mordred who came to kill Roland in his sleep. He is torn in half and impaled on a tree limb however, Stephen King hints that Oy will be found in the same universe that Susannah travels to and will be in some form of a dog.

Roland Deschain, son of Steven Deschain, was born in the fictional Land of Gilead. Roland is the last gunslinger, charged with finding the Dark Tower. This quest is obsession, monomania and geas to Roland: the success of the quest is more important than the lives of family and friends. He is a man who lacks much imagination, and this is one of the stated reasons for his survival against all odds: He can't imagine anything other than surviving to find the Tower.

The Drawing of the Three, in which Roland encounters three doors that open into New York City of our world in different times. Through these doors, Roland draws companions who will join him on his quest, as the Man In Black foretold. The first to be drawn is Eddie Dean, a drug addict and a first-time cocaine transporter. Eddie lived with his older brother and fellow junkie Henry, whom Eddie revered despite the corrupting influence Henry had upon his life. Roland helps Eddie fight off a gang of mobsters for whom he was transporting the cocaine, but not before Eddie discovers that Henry has died from an overdose of heroin in the company of the aforementioned mobsters (after which the mobsters decide to chop off Henry's head). It is because of Eddie's heroin addiction that he is termed 'The Prisoner', and that is what is written upon the door from which Roland draws him.

Roland also acquires medicine for his infection during the trip to Eddie's world, but this only temporarily quells the fever.

Eddie passes through the door into Roland's world, and faces the typically horrible withdrawal symptoms, but also shows an affinity for the ways of the gunslinger. Unwillingly at first, and somewhat forcibly, Eddie becomes Roland's companion through Mid-World, and soon falls in love with (and marries, in a way) Susannah, the next member of Roland's ka-tet.

During the attack on Algul Siento during the final novel, Eddie is killed by Pimli Prentiss, the master of the Breakers, via a shot to the head. Susannah is quite obviously distraught by this event, and eventually has Patrick Danville draw her a door to another world. Susannah crosses over into a world where an Eddie who strongly resembles "her" Eddie is alive and well and living in New York, along with his brother Jake (both now named Toren).

Roland also notes that Eddie's character strongly resembles that of Cuthbert's, a gunslinger of Roland's past, and one of Roland's greatest friends. The character of Cuthbert is mentioned in Browning's poem and is described most fully in Wizard and Glass, although he is first mentioned in The Gunslinger.

Also hailing from New York City, Susannah is an African-American (although owing to the fact that she is from a New York of 1964, she prefers the term, "Negro" [see top of article where it states that Negro was preferred prior to the 1970s] over the appropriate term of Eddie's when, "Black") woman with two major afflictions: her legs below the knees were severed in a subway accident (although not really an accident), and a childhood head injury (again, not really an accident) left her with Dissociative identity disorder. She is "The Lady of Shadows", the second companion predicted by Walter to be drawn through to Roland's world via the mysterious doors.

Initially, her dominant personality is that of Odetta Susannah Holmes, a sweet, well-mannered woman active in the civil rights movement. At times, however, she is taken over by Detta Susannah Walker, a murderously psychotic but incredibly crafty and strong willed woman whom neither Eddie nor Roland can control. After an incident at the beach with the lobstrosities, where Roland forces her two selves to see each other for the first time, her personalities are melded into one, and she becomes Susannah (later Susannah Dean, wife of Eddie).

During the drawing of Jake, she seduces the demon of the doorway in order to distract it and afterwards, she falls partially pregnant. Susannah shares the experience of her pregnancy with a demon-turned-mortal named Mia, resulting in Susannah housing another personality in her mind. Mia takes over Susannah's body (and melds with it, giving her legs for a short while), to NYC circa 1999 to help give birth to the demon child.

Susannah is the last of the Humans of his ka-tet to leave Roland (and the only one to survive in a Keystone world), having been given the chance to return to another form of Eddie and Jake in a parallel world.

Jake is the symbolic (and later adopted) son of Roland. He is originally from New York, circa 1977, but dies at the hands of Jack Mort (who Jake initially sees as Walter) and ends up in Roland's world as a result. Jake's given name is John, but he prefers to be known by Jake, and is called "'Bama" by his house-keeper only. They travel together in pursuit of the Man in Black, developing a strong bond along the way. However, in order to reach the Man in Black, Roland let him fall to his death.

The eleven-year-old boy Roland left to die reappears in The Waste Lands due to a paradox. Since Roland (in The Drawing of the Three) prevented Mort from shoving Jake into traffic, he never died, therefore he never appeared in Mid-World and was never left to die under the mountains. Jake and Roland, however, can remember both timelines, and the knowledge is slowly driving them insane.

In the first half of The Waste Lands, Roland's ka-tet figure out a way to draw Jake into Mid-world where he belongs (and thus finishes the real Drawing of the Three). Eddie is driven to whittle a key out of wood as they approach a Speaking Ring, where Eddie draws another door into the ground, this one guarded by an invisible demon. Susannah distracts the demon by allowing it to copulate with her, while Eddie perfects the key and opens the door. On the other side, Jake has been led to an abandoned house (by a past-version of Eddie himself) filled with evil spirits and a horrendous gate-keeper, but fights through them (with a bit of timely assistance from Roland) to reach the door. Once in Mid-World again, Roland's and Jake's memories are merged and their descent into insanity abated. Unfortunately, Susannah will pay the price for her distraction of the spirit.

While crossing the desolate city of Lud, Roland promises to come for Jake, despite it appearing that he may have to sacrifice Jake again to ensure their safe passage. Despite the danger, he rescues Jake, reaffirming the father-son bond that has grown between them. Like Eddie and Susannah, Jake shows amazing aptitude to the way of a gunslinger.

Jake is the second member of the ka-tet to die when he sacrifices himself to save Stephen King (a character in his own series) from certain death by putting himself between King and the van meant to take his life. An alternate version of Jake is encountered later by Susannah Dean.

Roland also notes that Jake strongly resembles Alain, another gunslinger, in using a psychic skill referred to as the "touch". Alain is described mostly as his time with Roland as a teen in Wizard and Glass.

Cuthbert is Roland Deschain's childhood friend, cousin, and a member of his original ka-tet. Cuthbert, often called Bert, is first featured in The Gunslinger, but he does not play a major role in the series until Wizard and Glass, the fourth volume in the series.

During the battle of Jericho Hill, Cuthbert is shot through the eye by an arrow fired by Randall Flagg.

Alain is one of Roland's original ka-tet, and along with the gunslinger and Cuthbert is evacuated to Mejis in Wizard and Glass for safety, due to the ongoing war against John Farson. Alain is strong in the 'touch', which appears to be a Mid-World form of telepathy or other mental power.

After Mejis, Alain joined Roland, Cuthbert and Jamie on their quest for the Dark Tower.

Shortly before the battle of Jericho Hill, the last stand by the gunslingers of Gilead against Farson's men, Alain was accidentally killed by Roland and Cuthbert, mistaking him for an assassin.

Jamie De Curry was a member of Roland Deschain's original ka-tet. He was the first to discover Roland's plan to fight Cort. He seemed to be characterized by a birthmark. He was killed by a sniper at the Battle of Jericho Hill.

Teacher of Roland's original ka-tet. Roland earned his guns by defeating him with the hawk David, who was killed in that battle. After Roland's challenge, Cort laid in his cabin for a week in a coma, being tended by two nurses. He also fancied calling the prospective gunslingers, "maggots".

Susan Delgado appears in "Wizard and Glass", the fourth book of the series. When Roland is sent away for a mission from Gilead by his father, he meets Susan Delgado. Her father was killed in a horseback riding "accident", and Susan is being forced by her aunt to be the gilly-girl (concubine) of the mayor of her town. Before she is to sleep with the mayor, she falls in love with Roland and plans to run away with him. She saves Roland's group from imprisonment and possible execution. Accused of killing the mayor, she is burned at the stake by the townspeople and her aunt. At the time, she is pregnant with Roland's first child. Roland admits that Susan Delgado was (and in many ways, still is) the love of his life.

Callahan is the "damned" priest who first appeared in the novel 'Salem's Lot. He makes his first appearance in the Dark Tower series in Wolves of the Calla, although his involvement in the series was hinted at in the afterword to Wizard and Glass. After being infected by the vampire Barlow, Father Callahan spends time in a homeless shelter that he later runs. Callahan made it a goal to get even with the vampires for what they did to his partner. He is aided in this due to his ability to spot the vampires; since Jerusalem's Lot (and the forced taking of some of the vampire Barlow's blood) he has been able to tell who is a vampire. He enters Mid-World after jumping from a window escaping the agents of the Red King, then arrives at the Way Station from the The Gunslinger (right after Jake & Roland left). He assists the ka-tet (becoming a partial member) in the Battle against the Wolves, helps Susannah's rescue mission from 1999 New York, sacrificing himself so that Jake may live, and making his final stand in The Dark Tower VII against the can-toi (low men) and vampires. Callahan kills himself before allowing himself to fall at the hands of the vampires in the Dixie Pig.