Berzerk by Stern Electronics, released in the arcade in 1980 and porting to popular consoles (Atari 2600 and its ilk)a couple of years later.
A revolutionary maze-crawling game, Berzerk put you in control of a little stick-guy who was being stalked by robots. Each level is a simple room filled with enemies who'd love to blast you (or touch you) - and the maze walls are lethal as well. Apparently there are 64,000 levels. Um.. that's a long game.
See that smiley face in the picture up there? This is the game's main antagonist, lovingly known as Evil Otto. Linger too long in a level and this monster shows up, happily bouncing toward you like some sort of 70s-icon grim reaper. Unlike the robots, Otto is invincible, and he is also faster than them. It is worth a mention that he doesn't seem to be impeded by walls and the like, either. You don't wanna be dilly-dallying to much, or Evil Otto will have you for lunch!
Most memorable of the game was that it featured a digitized voice, which was particularly creepy to hear in a video game of the time. "Intruder alert!" still sends a chill down my spine even now!
Games like Berzerk are practically laughable to look back on now - this is really getting primitive - but there was a time when this was quite revolutionary, and games like this would charge a player's imagination. The feeling of stress and risk/reward in a title like Berzerk was great (compared to the simpler "space shooters" at the time) and being able to control something actually resembling a person gave one my sympathy for/connection with their onscreen avatar, something that was also very new at this time.