Short answers, pulled from the story.
The first-person perspective renders the graphical view from inside a device or vehicle controlled by the player character. This viewpoint displays what the player's avatar would see through its own eyes without showing their body.
The initial development of Maze War probably occurred in the summer of 1973 with multiplayer capabilities added later that year and fully networked in the summer of 1974. Spasim was originally developed in the spring of 1974 with a documented debut at the University of Illinois the same year.
Wolfenstein 3D appeared in 1992 after id Software improved technology used in Catacomb 3D to add support for VGA graphics. It introduced conventions including collecting weapons switchable using keyboard number keys and ammo conservation.
Doom appeared in 1993 refining the Wolfenstein 3D template by adding support for higher resolution and improved textures. It allowed any inclination for walls unlike the grid based system where walls had to be orthogonal in Wolfenstein 3D.
Electro-mechanical racing games had been using first-person perspectives since the late 1960s with Kasco's Indy 500 appearing in 1968. The use of first-person perspectives in driving video games dates back to Nürburgring 1 and Atari's Night Driver in 1976.