An affable fellow, Miguel is the last resort for people down on their luck, buying what they offer at reasonable prices and selling them for a profit. His pawn shop has been in the family for at least three generations. In fact, Miguel took over the business when his grandfather lost his life to the Fiends. He has since built up an impressive collection of odds and ends.
The death of his grandfather has resulted in Miguel having a deep hatred for the Fiends, just as much as the other residents hold a grudge against the vicious raider gang, for the fear of the next potential attack.
Miguel hates Fiends, presumably because they killed his grandfather and are a threat and a nuisance to Westside and will talk about "those Fiend junkies over at Vault 3," voicing his opinion to "kill them all."
Miguel's dialogue in the G.E.C.K. suggests that Miguel's early name may have been Angelo. This is further reinforced by the early version of The White Wash's quest objectives, some of which refer to his pawn shop as "Angelo's Pawn Shop."