Arnold Schwarzenegger has been in four Terminator movies (T1, T2, T3, and Terminator: Genisys). In 1984, Arnold was tall and Arnold was muscular, and James Cameron wanted his scary killer cyborg from the future to be tall and muscular, so it was a no-brainer to cast Arnold, right?
Not necessarily. Arnold also came with his Austrian accent. James Cameron could have easily cast a made-in-America bodybuilder to play the Terminator, but for whatever reason, Cameron didn’t; nor did Cameron dub Arnold’s spoken lines (as was done in Hercules in New York). Okay, fine, so here’s this killer machine who speaks with an Austrian accent, and nobody notices. Arnold’s accent wouldn’t be so bad a problem for the Terminator movies except that they have never explained why a machine whose purpose was to infiltrate and to kill humans in Los Angeles of the future would have an Austrian accent.
I must presume that in the world of the story, Skynet did not simply invent the 800-series Terminator, but instead modeled the Series 800 after some tall, muscular Austrian. But who? It’s a complete mystery who this man was, and why Skynet chose him as the model instead of, say, Steve Reeves or Charles Atlas.
Well, it might be an mystery whom the Terminator was modeled after, but it won’t be a mystery to readers of The Inseminator whom my evil cyborg from the future is modeled after. My characters [Sarah] and [Kyle] seek out a certain Austrian man who looks and sounds exactly like the Inseminator, because this tall, strong Austrian man might know how to defeat the Inseminator.
I’m currently working on the next-to-last chapter of The Inseminator. The book will be out soon.
Hasta la vista, babies.
EDITED TO ADD (2017.08.14): Like I said, there is no canonical explanation (meaning, in any of the movies) of who was the model for the 800-Series Terminator. But in T2: Infiltrator, an uncanonical novel by S. M. Stirling, the story holds that the Terminator is based on “former counterterrorism operative Dieter von Rossbach.”