Chao are small creatures from an unknown location on Mobius. Although little is known about them in Sonic the Comic, they have appeared in many video games, most notably in their debut in Sonic Adventure.
The Chao made their Sonic the Comic Online cameo debut appearances in Part 2 of The Syndicate. The first one could be found in a jar alongside many classic STC exhibits, although it was unclear whether or not this particular Chao was still alive. A robotic version existed as Omochao, a friendly guide to the Death Carrier. Unfortunately, it was eaten by a Rexon Badnik. Another Chao appeared in the bonus feature Comic-Strip by Bakasam. This one was Cheese the Chao, friend of Cream the Rabbit. Unfortunately, in what seems to be a recurring event, Cheese was also eaten, this time by Cream. However, Comic-Strip is not considered STC canon and was written for humour only.
The Chao made a full debut in Night of the Livid Pet, the first part of which ran in Issue 269. Here, the Chao were marketed as robotic toys by a pair of scheming traders who knew full well they were living creatures- by the time their con was discovered, they had already moved on to the next town. During the course of the story, the captured Chao were accidentally freed and made their way into the Museum of Mobian Machinery where, using their amazing adaptive powers, they took on the properties of all manner of deadly Badnik foe, causing a huge problem for Tails and Amy Rose.