Short answers, pulled from the story.
First-person perspective in video games renders the world from the viewpoint of the player's avatar, as if looking through the character's own eyes. Players typically cannot see their avatar's body, though they may see the avatar's hands or weapons. It is one of the two dominant graphical perspectives in games, alongside third-person.
The two leading candidates for the first first-person shooter are Maze War and Spasim. Maze War's initial development probably occurred in the summer of 1973, while Spasim debuted at the University of Illinois in the spring of 1974. The exact priority is uncertain because Maze War's own developer cannot remember the precise dates of its creation.
Doom, released in 1993, refined the template established by Wolfenstein 3D with higher resolution, improved textures, walls at any angle, height variations, and lighting effects. It popularized competitive multiplayer matches called deathmatches, introducing that word into the video gaming lexicon. The source describes Doom as the most important first-person shooter ever made.
The Quake series, starting in 1996, and the 1998 title Half-Life, which used Quake's engine technology, helped establish the mouse and WASD key combination as the standard control method for first-person games on personal computers.
Motion sickness in first-person games results from a disconnect between the visual motion displayed on screen and the player's actual physical stillness. The perspective also makes it difficult to judge jumps accurately because the visible avatar body that would normally provide spatial reference is absent.
First-person perspectives in electro-mechanical racing games date back to Kasco's Indy 500 in 1968 and Chicago Coin's Speedway in 1969. The transition to video-based driving games came in 1976 with both Nürburgring 1 and Atari's Night Driver adopting the driver's-eye viewpoint.