The important characters in the carriage in "Because I could not stop for Death" are the speaker and Death. While Death is not a person, it is personified as a character in this poem, and is able to perform human actions, such as stopping a carriage. It could be argued that Immortality is also a character in the carriage, but it is only mentioned once at the beginning of the poem, and can be read as a state of being, rather than a character.