The characters in this poem are Death and the female speaker (a persona that Dickinson assumes). There is also Immortality, although Immortality is more of an abstraction than a character.
The speaker is figured as already dead, and she recalls the day that Death came for her.
Because I could not stop for Death -
He kindly stopped for me -
The Carriage held but just Ourselves -
And Immortality. (1-4)
Death here is personified as a courtly gentleman who bears the speaker away in his carriage in which Immortality is also present. The whole drive is presented as a gracious outing with a genteel suitor and a third person as chaperon, eventually getting closer to the speaker’s present home, the cemetery. There is none of the fear or apprehension which is usually associated with death and dying, although there is perhaps an indirect moral that one should remain mindful of one’s inevitable demise, and not be too busy to think about it.
Dickinson herself was extremely mindful of death, as she experienced the deaths of many people that she knew, and it is one of the favourite themes in her poetry. This particular poem is one of her most celebrated, exhibiting her usual taut style and unusual approach to her subject. The poem creates a dreamy, almost surreal scene, mixing strangeness with a semblance of normality in its depiction of a journey through familiar places towards a stopping point more final than any other.