Adventure was a video game released for the Atari 2600 in the winter of 1979. The game introduced a number of innovative game elements that we now take for granted including play areas that are more than one screen (instead of keeping the play contained in a single play area like a tennis court or the like) and being the first game to feature enemies that continued to Move even when not visible to the player.
In addition to those innovations, it can also be about having the first video game Easter egg that was widely known at the time of the game's release. Unlike previous video games that had obscure Easter eggs that often went widely unknown until the video game was picked over in emulation (such as the Easter egg in 1976's Fairchild Channel F's Video Wizball ), Adventure's Easter egg was well known during the game's heyday. Most players were aware of the trick where you could pick up a tiny, almost invisible, one-pixel key and use it to enter the chamber where the programs name, Warren Robinett, was spelled out on the screen.
The Easter egg Not just a bit of vanity work either, it's an interesting look at Atari culture at the time. Atari had been pushing hard to brand games as just Atari products without putting game designers' names up on the marquee, so to speak. It was such a contentious issue that some of the top talent at Atari left the company about it, including David Crane and Larry Kaplan. Robinett's Easter egg was a bit of subversive work, making him his name on the game even though Atari didn't put his name on the cover.