Foo lions are powerful celestial creatures that serve the gods of Chaos and Good, along with those mortals that impress them.
Foo lions have long, bush-tipped tails, long, floppy ears, large mouths, shaggy manes, and broad noses. They often weave peony flowers in their manes. Their fur is typically golden, orange, or black. They have large, blunt heads with wide-set, bulging eyes. Their bodies are somewhat leonine, with thick fur and padded feet. Their forelegs are lion-like claws, while their hind legs are more canine.
Foo lions have been known to help mortals on the material plane, especially if the person they are helping is kind and benevolent, or if the cause appeals to the foo lion's sense of justice. However, a stay of more than a few weeks outside of their home realm is rare.
Many good creatures consider foo lions symbols of courage and strength. Military officials in the Beastlands, Mount Celestia, and in areas of the Material Plane embroider foo lions on their court robes. Statues of foo lions stand in front of many official buildings - some of these are enchanted so that a foo lion on its home plane can communicate through them. You can always ask a question of such a statue, but the foo lion won't always answer.
In a fight, a foo lion is zealous, but rational, able to break off and regroup if out-matched. They favor surprise attacks and seige tactics, and are quite patient.
Foo lions are said to be the spirits of petitioners who serve Chaotic Good deities, who have been given this form, and proxy status, as a reward for exceptional service.
It is believed that a foo lion only ages when they cease to perform good works, so younger foo lions often regard their elders as inferiors. Very ancient foo lions often move into isolated corners of the less-traveled planes to escape this derision.
Foo lions can eat any inorganic matter, and are especially fond of gems and precious metals. Platinum and silver are especially delicious to them. Foo lions who accompany adventurers often ask for a portion of the treasure to eat.
Foo lions are closely related to foo dogs - the lions are a more powerful type of foo creature. Foo lions don't dislike their lesser kin, but rarely associate with them.
Sources[]
Monster Manual II (1e)
Kara-Tur Monstrous Compendium (2e)
Planescape Monstrous Compendium I (2e)