Remy is a small rat with large brown eyes, grey fur, and a peach nose, ears, fingers, tail, and lips.
Before Kingdom Hearts III
At some point in time, "Little Chef" met Scrooge McDuck after he tried one of his dishes. As the small rat wanted to expand his culinary horizons, Scrooge took this as an opportunity and helped financed Le Grand Bistrot, in Twilight Town while encouraging the small rat to be his personal chef.
While exploring the woods between Twilight Town and the Old Mansion, Sora, Donald, and Goofy come to the rescue of a small rat being attacked by Heartless. The rat then take control of Sora using his hair to help him gather fruit that had been scattered during the attack. Sora helps the rodent and goes on his way.
Later, when Sora returns to Twilight Town, he encounters Scrooge McDuck and learns that he's opened a new bistro nearby. The head chef is none other than the rat Sora rescued, known only as "Little Chef." Sora agrees to help Little Chef by bringing him ingredients to prepare new menu items. When the time comes to prepare a new meal, Little Chef hops on Sora's head and takes control of his body by pulling on his hair.
Remy is based on his respective character in the 2007 Disney-Pixar film Ratatouille where he is the hero of the film. Ratatouille is an original film, but certain elements are based on real life, such as Auguste Gusteau's character being based on real life chef Bernard Loiseau.