Wirth did it before BCPL in EULER, but virtual machines of various kinds predate EULER; Schorre's META-II output a textual assembly language for a fictitious processor, and Short Code predated that, but was intended to be written by hand. Simulators for one real computer on another were already commonplace by the 01960s, so that you could keep running your programs for an obsolete machine, and I don't remember anyone specifically saying so, but I would assume that designers of planned computers were writing such simulators for their designs by the end of the 01950s.