The speaker
The speaker's identity is unclear—it's not known why he's on the train going to London, or how he personally relates to the subject of marriage. His view of the ceremony is cynical, however, and he views the rest of the passengers with a sort of ironic detachment.
The wedding-goers
The anonymous wedding-goers are homogenous enough to be considered one character, portrayed on the whole as shallow, artificial, and silly.