One-eye is a pale gray she-cat who is virtually blind and deaf. A knotted scar covers the lid of her missing eye, and her remaining eye is yellow.

One-eye was a Thunderclan elder who served as a warrior under Pinestar's and Sunstar's leaderships in the forest territories. Whitekit and Specklekit were born to Harepounce and Stagleap but were later fostered by Rainfur after their mother died during the Great Hunger. Whitepaw was mentored by Smallear, though her cloudy eye didn't prevent her from becoming a warrior, later named White-eye. She gave birth to Sparrowpelt's kits, Mousekit and Runningkit. When she retired to the elders' den, her name was changed to One-eye. One-eye and her mate, now named Halftail, lived in the elders' den together during Bluestar's and Firestar's leaderships, where she also taught Firestar about the name changing ceremony. She later joined StarClan after her death.