Pac-Man (Arcade, 1980)

The story of Pac-Man (1980) goes that the developers at Midway noticed that the bulk of their audience was male, and not wanting to miss out on the potential for more money, they sought to make a game that would appeal to women.  In order to properly gauge what women would find appealing in a game, the designers would casually listen in on ladies' conversations, and made a few discoveries.  These women talked mostly about food, so they decided to make a game based around it.  The goal of Pac-Man is not to kill everything on a screen to advance, but to eat all of the pellets in a maze, whilst avoiding ghosts.  By eating one of the larger power pellets, Pac-Man would be granted the temporary ability to eat ghosts.  He himself is shaped like a pizza, and each level is denoted by a fruit.
Gaming is an industry that is still to this day idiotically marketed mostly to men.  This is poor marketing since statistically, 60% of all people who play video games and use the internet are female.  Pac-Man was a groundbreaking success because it found a gender neutrality that allowed Midway to target the entire audience of gamers at the time, and is possibly the catalyst for bringing women into the gaming mainstream.  Technology is always typically attributed to be masculine, so games targeted to men are more likely to be combat-driven and complicated in design.  Pac-Man uses one stick, is simple in design, but becomes difficult in practice.  Theoretically, the game should go on forever, but a programming glitch makes the game unplayable on the 256th stage.
Pac-Man inspired a glut of imitators, which inspired some lawsuits.  A game for the Magnavox Odyssey 2 called KC Munchkin, which was a blatant copy, was tried for copyright infringement.  Other games, which were able to get around this by making slight changes to the gameplay, included Mousetrap and Alien for the Atari 2600 (Yes, a game based off of the movie Alien was a Pac-Man clone).  Consumers were not fooled by most of these titles, as the original Pac-Man was still better than all of them.  The hype died off in 1983, when a rushed and poorly made port came to the 2600, appropriately sounding the end of that age in gaming to usher in the age of Nintendo.
The biggest influence Pac-Man had on the industry was to introduce one of the first and most well-lasting gaming mascots into the public conscience.  Before that, you played as a ship or some kind of indescribable shape.  Pac-Man was a character that (although basic) you could latch your sympathies onto.  There was some real conflict between the four ghosts (whose motivation is still questionable) and the round, hungry protagonist.  for the first time, gamers felt like they were playing as someone, a trait in gaming that persists strongly to this day, to the point where it is expected as a given.