Lastly Expeditionary Force series from Craig Alanson.

Based in near future Earth is attacked and partly enslaved by Apex species to fight their wars. Joe Bishop moves up the ranks in this future war by ingenuity and mostly dumb luck. Discovers an ancient AI who helps him escape and later fights on Earths side to fight all the Apex species. The AI is known as a complete Asshole and constantly pulls pranks on Joe. This series has a big following.