Quake II is a 1997 first-person shooter video game developed by id Software and published by Activision.

In contrast to the first game, which featured a combination of science fiction and fantasy elements, Quake II entirely drops the latter elements and is set during humankind's war against a rogue alien race known as the Strogg, half-mutant half-machine creatures whose homeplanet, Stroggos, is the target of the humans' invasion force.

The player takes the role of a space marine (referred to as Bitterman) as he crash-lands on the planet and, being the last survivor of his squad, is tasked with completing a series of missions to cripple the Strogg and end their plans to conquer Earth.

[14] Quake II received critical acclaim on its release, and similarly to its predecessor is generally considered to be one of the best video games ever made.

First, the player is given mission-based objectives that correspond to the storyline, including stealing a Tank Commander's head to open a door and calling down an air-strike on a bunker.

Bitterman survives because another Marine's personal capsule collided with his upon launch, causing him to crash far short of the landing zone.

But after numerous failed attempts, the team at id decided to stick with Quake II and forgo the Gothic Lovecraftian horror theme from the original in favor of a more sci-fi aesthetic.

[21] Artist and co-owner Adrian Carmack had said that Quake II is his favorite game in the series because "it was different and a cohesive project".

[24] Quake II's game engine was a popular license and formed the basis for several commercial and free games, such as CodeRED: Alien Arena, War§ow, SiN, Anachronox, Heretic II, Daikatana, Soldier of Fortune, Kingpin: Life of Crime, and UFO: Alien Invasion.

The source release also revealed numerous security flaws[27] which can result in remote compromise of both the Quake II client and server.

As id Software no longer maintains Quake II, most third-party engines include fixes for these bugs.

In May 2004, Bytonic Software released a source port of Quake II (called Jake2) written in Java using JOGL.

[30] In December 2018, Polish programmer Krzysztof Kondrak released the original Quake II v3.21 source code with Vulkan support added.

[31][32] A new source port of the game, titled Quake II RTX, was announced by Nvidia in March 2019[33] and was released on June 6 for Windows and Linux on Steam.

[34][35] The source port, provided free of charge, includes the three levels present in the original Quake II demo,[d] but can be used to play the full game if its data files are available.

id initially wanted to set it separately from Quake, but for legal reasons (most of their suggested names were already taken), they decided to use the working title.

[42][43] In both cases, the core gameplay was largely identical; however, changes were made to the game sequence and split-screen multiplayer replaced network or Internet play.

[44][45] For example, many short airlock-like corridors were added to maps to provide loading pauses inside what were contiguous areas in the PC version.

He travels through the swamps and bypasses the compounds outer defenses and enters through the main gate, finding his squad just in time to watch them get executed by Strogg forces.

The section of the game that takes place on the Moon Base has low gravity, something that was previously used on one secret level of the original Quake.

[56] It comes with fourteen single-player levels, ten multiplayer maps, five additional music tracks, five enemies, seven power-ups, and five weapons.

One of the marines who managed to land, Stepchild, must now make his way to the Gravity Well to destroy it and free the fleet above and disable the entire defenses of the planet.

[60][61] Patrick Baggatta of IGN gave the expansion 7.5/10, describing it as similar to the original, but noting occasionally confusing map design.

[57] Elliott Chin of GameSpot gave the game 7.9/10, citing it as decent for an expansion and praising the monsters and enhanced AI.

A large number of mods, maps, graphics such as player models and skins, and sound effects were created and distributed to others free of charge via the Internet.

Praising its interconnected levels, new weapons, enemy design, soundtrack, and the ability to play as a female character in multiplayer mode (which they called "an overdue nod to the growing number of QuakeGrrls"), they gave it a perfect 5.0 out of 5 in all four categories (graphics, sound, control, and funfactor).

[69] AllGame editor Michael L. House stated, "the beauty of Quake II is not in the single-player game, it's in the multi-player feature.

The editors wrote that "for pure adrenaline-pumping, visceral, instantly gratifying action, Quake II is the hands-down winner.

"[84] Quake II entered PC Data's monthly computer game sales rankings at #2 for December 1997, behind Riven.

[86] The following year, Quake II secured fifth place on PC Data's charts for January and February 1998,[88][89] then dropped to #8 in March and #9 in April.