If you're a fan of the Metal Gear video game series, an obvious Halloween costume choice would be Solid Snake, the protagonist of nearly all of the games. However, an even better option would be Big Boss, aka John, Ishmael, Vic Boss, The Man Who Sold the World, and Naked Snake, among many other aliases. He's was once a good man, but better known as the nemesis to Solid Snake.
The below costume by YouTube user Erick Zeros showcases Naked Snake in his good era, in Metal Gear Solid 3: Snake Eater. It's an easy tough-guy costume. You just need a long-sleeved black turtle neck and army attire, preferably a button-down shirt and matching camo shorts, most of which you can pick up any military surplus store.
From there, it's time to add gear, including army-esque canteens, bags, and other easy-to-carry items across a desert. Add a sand-colored head band, an eye patch, and dangerous knives, and you're ready to go. Again, most of these items can be found at a military surplus store, so do what you can to match the look as closely as possible.