It's the way games have been made for years, but it also means that, for the most part, every character in Call of Duty is a true-to-life replica of its voice actor. So, it comes as no surprise that Simon 'Ghost' Riley is the digital embodiment of Samuel Roukin.
The comic series is set before Ghost became a member of Task Force 141, with events from both before and leading into the game, focusing on the origins of the character, his skull-like mask, and why he calls himself Ghost.