Thief

The Thief series launched in 1998 with Thief: The Dark Project on PC, and effectively defined the first-person stealth genre. Rather than relying on firepower, it built on sneaking, the interplay of light and shadow, and sound cues — playing as the thief Garrett, you tried to stay unseen and unheard, with weapons only ever a last resort. The game unfolded in a dark, steampunk-tinged world known as the City, where medieval architecture blended with mechanical contraptions and occult factions, giving the series a distinctive atmosphere unlike the shooter hits of its time.

The 2000 sequel, Thief II: The Metal Age, refined that stealth mechanic further and is still cited by many players as the series' peak thanks to its intricate, open-ended mission design. Thief: Deadly Shadows in 2004 brought the series to Xbox for the first time and paired the mission structure with a walkable hub version of the City, though console limitations forced some of the larger levels to be split into smaller chunks. Despite that, Thief remained an important forefather of the immersive sim genre, influencing later stealth games and leaving an emphasis on sneaking and improvisation that echoes through titles like Splinter Cell and Dishonored.