Portal grew out of Narbacular Drop, a 2005 freeware game made by students at DigiPen Institute of Technology. Valve developer Robin Walker saw it at a career fair and Valve's president Gabe Newell offered the team jobs to develop it further. The portal mechanic was kept, with its orange and blue endpoints, while the princess-escape setting was replaced by Aperture Science. Valve's writers, working with Half-Life writer Marc Laidlaw, created GLaDOS, a polite but sinister AI. Many odd details came from testing, such as the cake reward, which was chosen after a team meeting about which philosophy the game should follow. The team reached the design of the Weighted Companion Cube by making players attach emotionally to a box.

Hampi is a UNESCO World Heritage Site in Karnataka, India, with more than 1,600 surviving remains spread over 4,100 hectares. It was the capital of the Vijayanagara Empire from 1336 to 1565. Travellers from Persia and Portugal described it as a prosperous, wealthy and grand city with temples, markets and farms along the Tungabhadra River. By 1500 it was estimated to be the world's second-largest city after Beijing, and probably India's richest at the time. In 1565 a coalition of Muslim sultanates defeated the Vijayanagara Empire, its capital was conquered and destroyed, and the city was left in ruins. Hampi remains a religious centre, with the active Virupaksha Temple at its heart.