Stealth-action video games fill out a genre that asks its players to surreptitiously navigate through an enemy-occupied area while maintaining discretion and avoiding detection. Popularized by Hideo Kojima’s Metal Gear series -- beginning in 1987 -- they have seen the birth of many venerated franchises and been key participants in the mechanical cross-pollination of tropes throughout the rest of the medium. Of particular interest are the history, common heritage, and subsequent maturation of the genre, and how its development shapes not only stealth-centric games, but action and adventure titles going forward.

The genealogy of stealth games

The history tree (above) highlights efforts that either introduced or revised the conventions of the genre. Of course there are other games that incorporated components of stealth and evasion, but the games of chief interest, and those that I will now discuss, are the ones that introduced, expanded, and even standardized certain mechanics of covert action in stealth games. These are the salient games of the stealth genre, which represent significant milestones in the genus’ timeline.

The lineage of stealth-based video games goes back a long way. The act of eluding a predatory aggressor and evading them if noticed is the "flight" component in humanity's fight-or-flight response. It's a vital behavioral mechanism of survival that predates mankind. Avoiding conflict and violent confrontation is such an engrained part of the human condition that even children display a keen recognition of it. Thus, it is only natural that stealth appeared on the scene so early on in the history of video games.

One of modern stealth game's common ancestors is Castle Wolfenstein (Muse Software, 1981), originally released for the Apple II computer. In the game, participants must progress through a series of rudimentary corridors with the aim of reaching end zones and collecting secret war documents. Standing in the way of these exits are patrolling guards. The game arms the player with a gun, but ammo is scarce. Stronger enemy types take a considerably more ammunition to kill, which subsequently makes it increasingly difficult to win a gunfight. Dead guards leave behind ammo, keys, and bullet-proof vests.

Searching a body.

The firsts on Castle Wolfenstein’s feature list:

• Disguises: The player can find SS uniforms to wear. These will fool the base guard type, but not higher-ranking officers.
• A.I. alarm triggers: Sounds the player makes can alert the guards. They will only react to the sounds of gunfire, grenades, or the absence of a blending uniform. Once they the detect the player, they rush to confront the player.
• Holdups: If the player draws a firearm before a guard does, they can frisk the guard for resources.

Castle Wolfenstein serves as a model of convention for the stealth genre with many features that other games came to adopt. Among these descendants is Metal Gear (Konami, 1987), a prototypical work which began an illustrious franchise that was instrumental in stealth games coming to prominence.

Series architect Hideo Kojima created and designed Metal Gear. It incorporated core elements from Castle Wolfenstein, including alert patrol guards (with a straight line of sight to detect players) and the option to shoot enemies. It also added new features and included a more technically refined presentation. The feature set included the following:

• Overhead view
• Multiple alert modes:
       1) Only enemies in the player-occupied screen will attack.
       2) Enemies descend on player from other screens.
• Subtle noise detection: Guards become suspicious of close-range player movement and unsilenced gunfire.
• Silenced firearms: For long range stealth kills
• Cameras and infrared sensors: Obstacles that can spot players and alert guards.
• Melee attacks: Close-range stealth kills.
• Varied weapon arsenal: Including heavy weapons like a rocket launcher.
• Boss fights
• Hostage rescue
• Radio transceiver: A device that allows the player to correspond with ally characters.
• Safe screens: Areas of the level where pursuing guards do not follow.

The game's release didn’t send shockwaves through the industry or garner enough of a sparkling reception to put stealth games on the map, but it was successful enough to warrant a sequel. Metal Gear 2: Solid Snake (Konami, 1990) maintained the design framework of its forebearer while also introducing some noteworthy additions:

• Radar window: Highlights enemy locations and outlines level geometry.
• Continuous screens: Levels where seamless movement between areas is not confined to one screen.
• 45-degree field of vision: Guards have better sight.
• The ability to crouch: Provides a tactical advantage to hide in new hiding spots and reduces movement noise.
• Timed alert and evasion system: If the enemy spots the player, a countdown timer appears on screen. For the timer to reach zero, the guards cannt notice the hero again for the duration of the countdown. Once the timer reaches zero, the guards return to their normal patrol.
• Distraction items: These include robotic mice that lure guards to a desired location.

Going prone to avoid detection. New radar in the top right corner.

It wasn’t until 1998 that stealth-based games captured the attention and esteem of a very broad audience. Most notably, Metal Gear Solid (Konami, 1998), Kojima’s third stealth action game, became a seminal work that propelled the genre forward and proved a critical and commercial success -- a feat its antecedents did not accomplish on this scale. It features polygonal graphics -- thanks to the Sony PlayStation -- and the game’s level design took advantage of this new dimension to create high and low areas, 360-degree player vision, and terrain topology. All of these made the player more vulnerable while also encouraging more recourse for stealth.