"The Cask of Amontillado" by Edgar Allan Poe is a short story tightly focused on the two main characters, Fortunato and Montresor, the narrator of the story. The minor characters function almost as if they were scenery, setting a backdrop for the story rather than being integral parts of the plot.
Montresor mentions a wine seller Luchresi, mainly to pique Fortunato's interest and inflame his jealousy as a motive to get him into the crypt. Fortunato says twice:
"Luchresi cannot tell Amontillado from Sherry."
This suggests that there is some element of jealousy or enmity in their relationship.
Montresor also mentions "British and Austrian millionaires", but they do not actually appear in the story.
As the story is set during Carnival, there are crowds on the streets, but Montresor guides Fortunato away from them and they are not mentioned directly. Montresor also has servants, but he has arranged that they attend the Carnival and so they are not present.
Luchresi the wine connoisseur is used as the bait to draw in Fortunato, and he should be considered a minor character even though he is not technically present in the story.
Fortunato's wife is referenced, but she too is not actually physically present in the story.
There are also some household servants who are referenced.