Reepicheep is a valiant talking mouse who stands around two and a half feet tall. Di spite his small stature, he is a courageous and skilled warrior who only thinks of battles and honor.
During the time when the Old Narnians were outlawed, Reepicheep lived in hiding and led a band of twelve mice. When Caspian arrived and pledged to overthrow the Telmarines and restore Narnia to the Narnians, Reepicheep is one of his most ardent supporters and fought bravely in the battles to deliver Narnia. He is seriously wounded in the Second Battle of Beruna, but Lucy restored him with her magic cordial. She could not, however, restore his tail which had been cut off, and Reepicheep seeks to give up his position as leader of the mice, because the tail of a mouse is it's honor and glory. But when the other mice pledge to cut off their tails as well if their leader is denied the privilege of having one, Aslan restores Reepicheep's tail because the mice had freed him of his bonds long ago at the Stone Table.
Once Caspian is crowned king of Narnia, he makes Reepicheep a Knight of Narnia. Later, when Aslan makes a door in the air for the departing Telmarines to use, Reepicheep volunteers to go through first as an example to others, but is told that he would only be captured and be put into a circus if he did so.
Three years later, Reepicheep joins Caspian on his east-ward voyage to find the seven missing Lords. While Reepicheep desires to aid Caspian in his quest, he is also searching for something else. When he was an infant, a dryad spoke a prophesy over his cradle, staying that he would find all he sought in the utter east. Reepicheep desired to sail as far east as possible and then travel alone, always going eastward.
Reepicheep was an invaluable companion on the voyage, and held in high regard by everyone, even by Eustace, who originally could not stand him and dared to even grab him by the tail and swing him in the air until Reepicheep administered a swift and sharp punishment.
When they reached Ramandu's Island, they found the remaining three lords in a deep sleep, but were told that they could not waken until they sailed as far east as they could, and then left one of their companions there, never to return. As this was Reepicheep's greatest wish, he readily volunteered himself, and once reaching the furthermost eastern shores, set off in his coracle alone, paddling ever eastward.
He was carried into Aslan's Country on a wave, and was never seen in Narnia again, but was the first to greet the Narnians at the Garden in Aslan's Country after the end of Narnia, many years later.