Hideo Kojima had the FOX engine developed for Metal Gear Solid V, because he was tired of game devs thinking they knew better than him. He’d ask for something specific, and the game devs would do it differently because they thought they knew better. So he created his own engine, to be able to go “fucking fine, I’ll do it myself.” Essentially, he was tired of having his ideas filtered through the game devs, so he created his own engine to be able to understand how the engine worked and have a more direct hand in the development.

And MGSV is one of the most well polished games in history. The story is a hot mess because there was some politicking tomfoolery between Kojima and the publisher... But the actual gameplay is top notch, and the game runs smooth as butter on even low-end systems, while looking amazing.

The irony is that Konami almost immediately abandoned the FOX engine, due to the aforementioned politicking. Kojima left the company, and the engine was quickly relegated to only being used for bad soccer games that Konami cranked out every year. Then once the PS5 came around, Konami didn’t want to update the engine, so they abandoned it entirely.