Chao first made their appearance in Sonic Adventure for the Sega Dreamcast in 1999 (December 23, 1998 for Japan) as a launch game. Chao (pronounced "chow") were seen to have existed since an ancient time, protected by a creature named Chaos; this was also the original guardian of the Master Emerald.
The player has been able to raise Chao for themselves in all the Sonic Adventure games, Sonic Advance games, and also Sonic Pinball Party. The Chao are an evolution of the 'A-Life' system that Sonic Team originally created in the Sega Saturn Game "NiGHTS into Dreams.." via small creatures called 'Nightopians'. (Nightopian section may come soon one day!)
You can raise Chao in-game in a special environment called "Chao World". In this Chao World you will find Chao Gardens, which are protected, enemy-free locations designed for raising Chao.
Chao hatch from eggs and grow through infancy into maturity. However, the way you care for your Chao will determine its physical characteristics, behaviour, personality, and way of life.
These Chao create a very unique ecosystem and learn and breed according to what you do. You must help your Chao to live by providing it with the necessary things such as food and attention.
Chao have become a very popular character within the Sonic series, helped also by the Sonic Adventure series being ported to GameCube, PC, PS3, and Xbox 360. Chao have appeared in a lot of different places, and I will try and cover all of these on the website.