These characters are only referred to in MT's narrative. "Him" is the husband of Judith Loftus, the villager whom Huck visits while dressed as a girl. Along with this "other man," he plans to go after Jim as a runaway slave for the $300 dollar reward that's being offered for his capture. Mrs. Loftus tells Huck that before they start after the runaway, they've gone to "get a boat" and "borrow another gun."
The Barrett Collection, UVA PS1305 .A1 1885b