The first door brings Eddie Dean, a heroin addict who smuggles cocaine for the Mafia. Since Eddie was headed deeper into addiction (at the hands of his brother) or prison (at the hands of the government), or worse (at the hands of his Mafia boss), he decides to throw his lot in with Roland, although with deep misgivings that he occasionally gives vent to in the form of angry outbursts.

The second door finds Odetta Holmes, a black woman who, like many of her contemporaries, is active in the civil rights movement, but unlike many of her contemporaries, is very wealthy and missing her legs as a result of a subway accident. Odetta also has a violent alter ego named Detta Walker of whom she is completely unaware. Roland and Eddie are forced to contend with both of these personalities when Odetta's body is forcibly abducted into their world.

The third door that Roland encounters brings not a new companion, but instead a new adversary for Roland named Jack Mort. This encounter results in the fusing of the personalities of Odetta and Detta to form a third woman, who will thenceforth be called Susannah.

Each of these people is essential for Roland to continue his quest. They are all part of a "ka-tet", defined as "one made from many" and "sharing the same destiny".