Short answers, pulled from the story.
The first-person perspective is a graphical technique where the game displays exactly what the player's avatar would see through their own eyes. This perspective often hides the character's torso and head to create the illusion of being the protagonist, with the player character's right hand firing a gun serving as the only visual proof of a human being within the digital world.
The summer of 1973 marked the beginning of a graphical revolution when developers began rendering maze corridors from a fixed perspective. Two competing titles, Maze War and Spasim, claim the title of the first true first-person shooter, with Spasim developed in the spring of 1974 at the University of Illinois.
The 1993 release of Doom refined the template by adding support for higher resolution, improved textures, and variations in height such as stairs and platforms. Unlike Wolfenstein 3D, which was limited to a grid-based system where walls had to be orthogonal to each other, Doom allowed for any inclination to create a far more believable 3D environment with flickering lights and areas of darkness.
The 1995 release of Descent used a fully 3D polygonal graphics engine to render opponents, departing from the sprites used by most previous games in the first-person shooter genre. Descent escaped the pure vertical walls graphical restrictions of earlier games, allowing the player six degrees of freedom of movement including up, down, left, right, forward, backward, pitch, roll, and yaw.
The year 1979 saw the release of FS1 Flight Simulator from Sublogic, which became a first-person staple for home computers and was followed up with Flight Simulator II in 1983. The 1989 release of Hard Drivin' from Atari Games was particularly influential, featuring fast filled-polygon graphics, a mathematical model of how vehicle components interact, force feedback, and instant replay after crashes.