Stealth & Perception

Castle Wolfenstein's Line-of-Sight Detection is the founding move and a genuinely strange one: it gives the AI a state of knowledge distinct from the game's. Once an enemy can be wrong about where you are, that wrongness becomes a resource, and every stealth mechanic since has been about shaping it.

1998 is the year the family resolves. Metal Gear Solid ships Graduated Alert States — unaware, suspicious, alerted, searching, resolved — which converts failure from a restart into a recoverable condition, then adds Explicit Detection Feedback so the player can see what the AI knows. Thief takes the opposite approach in the same year. Light-and-Shadow Stealth turns illumination into a measured resource and lighting from art direction into level design; Diegetic 3D Audio Information makes footstep material, distance, and occlusion carry real tactical data, promoting the ear to a primary sensor.

That split is the family's permanent argument: whether the system should be shown or felt. Metal Gear Solid's exclamation point and vision cones make stealth teachable and fair at the cost of admitting it is a machine. Thief's darkness gauge and audible stone floor keep the fiction intact and ask the player to build their own model of what the guard heard. Neither has won; most modern stealth games run both and let a difficulty setting arbitrate.

Ultima Underworld sits slightly apart, contributing Systemic Solution Space — consistent interacting systems in place of authored solutions — which is the immersive sim's founding contract and the reason its descendants keep escaping the stealth genre entirely. Assassin's Creed then moves hiding out of the shadows and into daylight with Social / Crowd Stealth, where behaviour rather than geometry conceals you.