Level designer

Level design, environment design or game mapping is a discipline of game development involving creation of video game levels—locales, stages, or missions. This is commonly done using a level editor, a game development software designed for building levels; however, some games feature built-in level editing tools. Level design is both an artistic and technical process.

In early days of video games, a single programmer would create the maps and layouts for a game, and a discipline or profession dedicated solely to level design did not exist.

Early games often featured a level system of ascending difficulty as opposed to progression of story-line.

The first game genre that required significant amounts of time to design areas were text-based games, such as MUDs. Often, promoted users were assigned to create new paths, new rooms, new equipment, and new actions, often using the game interface itself. ZZT is another early game notable for its user-accessible mapping and event triggering/scripting

1983's Lode Runner was one of the first titles to ship with a level editor, and its designer, Douglas Smith, reputedly paid neighborhood children to design levels for the game.

Doom (1993) and Doom II (1994) were two of the first games to attract focused game modding activity, and many WAD level files were made for them. One of the reasons was a clear separation between the level files and game engine itself.Half-Life, Quake 3, and many other games have notable mapping tools and communities focusing on user-generated content.

In certain games, such as roguelike games, levels may be procedurally generated. In these cases, the original game programmer controls how the variations of rooms and tunnels are formed, by tweaking the randomly seeded algorithms.

...
Wikipedia