The Spacewar! game was initially developed in 1962 by Steve Russell on a DEC PDP-1 minicomputer. It is said to be the first known video game installed on several computers and it was very popular in the programming community in the 1960s. It was ported and rewritten several times to different hardware architectures and complemented with additional features. Computer Space, the first arcade video game cabinet was a clone of Spacewar!
Wikipedia describes very precisely this space combat simulation game:
The gameplay of Spacewar! involves two monochrome spaceships called "the needle" and "the wedge", each controlled by a player, attempting to shoot one another while maneuvering on a two-dimensional plane in the gravity well of a star, set against the backdrop of a starfield. The ships fire torpedoes, which are not affected by the gravitational pull of the star. The ships have a limited number of torpedoes and supply of fuel, which is used when the player fires the ship’s thrusters. Torpedoes are fired one at a time by flipping a toggle switch on the computer or pressing a button on the control pad, and there is a cooldown period between launches. The ships remain in motion even when the player is not accelerating, and rotating the ships does not change the direction of their motion, though the ships can rotate at a constant rate without inertia.
Each player controls one of the ships and must attempt to shoot down the other ship while avoiding a collision with the star or the opposing ship. Flying near the star can provide a gravity assist to the player at the risk of misjudging the trajectory and falling into the star. If a ship moves past one edge of the screen, it reappears on the other side in a wraparound effect.
Therefore, the protagonists of the game are: