For as far as I can recall, Rorschach seems to be the start of this trend in popular media -- I'm sure it may have happened in a previous novel or film (I suppose an argument could be made for Albert Camus' Meursault in The Stranger, but I don't ever hear anyone talk about that in broader circles).

...But Moore is the first author I know of who went on record basically admitting he tried to make Rorschach a parody of Conservatism, but he just ended up making him based... and right.