Rob Gronovius
Non-movie books are Casca The Eternal Mercenary
Wow, that's a bulb going on!
I eagerly devoured the first dozen or so of the Casca series when they first came out in the '70s-'80s (about the same time as enjoying Don Pendleton's Mack Bolan 'the Executioner' series)...but sort of lost track after Sadler's death, when other authors picked up the franchise. Probably ought to go back and revisit them.
Enjoy!