We can give credit to Warren Robinett, the developer of the Atari 2600‘s Adventure game for the first known Easter egg. As Atari did not credit developers, he decided to showcase it on his own. He created a hidden room within the game that when entered would display "Created by Warren Robinett"
Easter eggs in computer programing are meant to be much like the cheerful holiday reference. They are a hidden (undocumented) set of commands that will result in a display or action, even a small game that is meant to be fun or amusing. Sometimes it’s a succession of keystrokes, a word or phrase that will deliver the resulting “Easter egg” or surprise response. You will find Easter eggs hidden in most types of software, from web browsers to video games and even in business software. Sometimes the result is to show credits to programmers and sometimes it is purely amusement.
Google programmers seem to love dropping these little colourful surprises for users to find. After a small “hunt” of my own, I came up with a couple amusing results: