Milko is the "little person" owner of the General's Store, and he does not realize he is small. In fact, he thinks he's about 6'7" and weighs in at a muscular 360 lbs. The Prisoner may find out from the locals that Milko drank too much of Hoover Dam's filtered and processed irrigation water before anyone could tell him it was not for human consumption. It might be best if the Prisoner just played along with Milko's delusions, especially if they want to do repeated business.
Milko has not appeared nor is he mentioned in any published game. He was to appear only in Van Buren, the canceled Fallout 3 by Black Isle Studios. It is not certain if he will appear in any future Fallout game.