Foil
Character Role Analysis
Gustav von Aschenbach and The "Other"
We give you the full lowdown on the figure of the "Other" in the "Characters" section as well as over in "Themes," but suffice it to say that this figure—or set of figures, to be exact—show up to mark Aschenbach's shift from respected, ideals-upholding writer to a man desperate for the approval of a fourteen-year-old boy.
Most obvious is the man on the boat (see 3.10-12) whom, when Aschenbach realizes that he is actually old and made up to look young, totally disgusts our main man. When Aschenbach turns into a version of this figure later on, just how much he's changed is really clear—the boat man is no longer "other" to Aschenbach, but of him.