Oracle of Delphi

The oracle is a skeleton or mummy-like creature which opens its mouth and released "green mist" when telling prophecies or speaking. It has never been known to leave the Camp, but has left the attic in which it resides only once. Normally, it won't speak of anything but prophecies.

History
The history of the Oracle of Delphi isn't easy to find out. It has been in Camp Halfblood's attic for a very long time, for millenniums, perhaps. This oracle has been mentioned in nearly every book at least once, even if just for a page or two. In The Titan's Curse, the Oracle leaves its attic to speak to Zoe Nightshade and tell her a prophecy to rescue Artemis. Many prophecies have been spoken from the Oracle, probably many that won't be remembered.