First tactical espionage game to allow pacifist completion

In Metal Gear Solid 3 it is possible to complete all missions, including boss encounters, by using non-lethal force. Protagonist Naked Snake (this is a prequel to the first Metal Gear) may exhaust his antagonists, or in one record-breaking case simply wait for them to die of old age. Consequently, Metal Gear Solid 3 became the first game that players obsessively aimed to complete without wilfully harming another living soul. However, if an enemy does die eventually, owing to an unfortunate chain of events, nobody seems to mind that at all.