|Before the Great War happened in the Fallout universe, the US government hired a company called Vault-Tec to design and produce a series of bomb- and research shelters known as vaults. Vault Boy is their mascot, and therefore he appears in their adverts, guides etc.
In real life, Vault Boy was originally designed by Leonard Boyarsky – One of the creators of the very first Fallout game from 1997. He based the character partly on Rich Uncle Pennybags – the Monopoly Man. Vault Boy characteristically has wavy, short, blonde hair and a blue jumpsuit with yellow details on it. Mostly he wears a giant smile, but he does have other expressions as well. (Poster-boys are allowed to be sad, believe it or not.)