Portal

Portal gave players a gun and asked them to think instead of shoot.

Released by Valve in 2007, Portal took the familiar controls of a first-person game and built them around puzzles instead of gunfights.

As Chell, players linked distant surfaces with two portals. Walking through one meant emerging from the other, carrying momentum across the connection. That simple rule turned solitary test chambers into problems of space, timing and movement rather than combat.

The idea grew from the DigiPen student game Narbacular Drop, whose team Valve hired. Portal transformed it into a tightly paced commercial game and wrapped the puzzles in an increasingly unsettling story shaped by GLaDOS.

It helped establish the modern first-person puzzle game as a recognizable form. Its influence can still be felt in games built around manipulating space in unusual ways.