IIRC the original idea for the Terminator was for it to have the appearance of a regular guy on the street, the horror arising from the fact that anyone around you could actually be an emotionless killer.
They ended up getting a 6 foot Austrian behemoth that could barely speak english. One of the greatest films ever made.
Lance Henriksen who ended up playing a cop in The Terminator was originally cast as the Terminator. But then Arnold was brought in and the rest is history.
Maybe as consolation, Cameron went on to cast Lance as the rather helpful android in Aliens.