William Weiher's 1967–68 TOPS-10 'make love not war' hack is the earliest documented software easter egg

software-historyeaster-eggstops-10stanford-ai-labwilliam-weiherauthorship

Between October 1967 and October 1968, William Weiher wrote a hack for Stanford AI Lab's PDP-6/10 systems that, on a specific input, printed "make love" and, after a pause, "not war." Rather than being removed, the hack was retained by DEC in official TOPS-10 operating-system releases, carrying an internal comment instructing engineers to "leave the above hack in for sales demos." Interviewed by Kate Willaert in 2021, Weiher confirmed his authorship without having anticipated its later significance: "Yes, I was the one that programmed this although I never imagined that anyone might think that this was the first 'easter egg'."

This predates Warren Robinett's 1979 hidden-room signature in Atari's Adventure — usually cited as the first video-game easter egg — by roughly a decade, and unlike Robinett's, Weiher's hack survived not by evading a publisher's policy but with the publisher's (DEC's) own sanction, folded into a sales pitch. See claim-robinett-hid-name-in-atari-adventure-as-uncredited-designer-signature for the comparison and entity-easter-egg for the term this hack is now cited as originating.