MIKE was brought to life by ELIAS TOBIN -- the last descendant of that dimension's JOHN TOBIN -- in an experiment that Elias never thought would work.
For years, Mike remained in hiding, studying Tobin's Spirit Guide (and other paranormal reference) with Elias, who eventually found another eager student in a young RAY STANTZ. The friendly Ray took to Mike right away, adopting the golem when an aged Elias finally passed.
Mike helped Ray and the Ghostbusters for years, taking over the bulk of casework when they grew too old to continue. He was estatic to learn there were new dimensions, certain this meant he would never be alone...