Normal mapping existed before Gears of War, but that 2006 release made it the expected standard for console game assets almost overnight. The technique involves sculpting an extremely high-polygon version of a model, sometimes 4 to 8 million polygons, then baking the surface detail into a texture that sits on a low-polygon game mesh. The result looks detailed without the performance cost of the full sculpt.
Epic's environment team used this workflow to put brick-by-brick surface detail on walls built from a few hundred polygons. The Locust Horde characters had skin pores, armour scratches, and fabric weave all stored in normal map textures rather than geometry. For freelancers, this changed what a complete asset delivery looked like. Suddenly a prop was not done when the mesh was done. You also needed the high-poly sculpt, the baked normal map, the ambient occlusion map, and the diffuse texture.
Clients who had been buying assets before this shift sometimes did not account for the extra time in their budgets. If you are scoping a prop or environment asset contract today, clarify explicitly whether the brief includes high-poly sculpting and baking, or just the game-resolution mesh. Those are two different scopes with meaningfully different time requirements.
The Gears of War pipeline became the template that tools like Marmoset Toolbag and Substance Painter were later built around. Knowing where that pipeline came from helps you explain your process to clients who are newer to commissioning 3D work.