She is the Gremory Clan's heiress after her oldest brother, Sirzechs, took the position of Lucifer. Rias is the sole daughter and youngest child of Zeoticus and Venelana Gremory, the aunt of Millicas Gremory, and the maternal cousin of Sairaorg and Magdaran Bael. Rias is a beautiful young woman with a voluptuous body, white skin, blue eyes (blue-green in the anime, season 1-3) inherited from her father, Zeoticus, and a buxom figure. Her body measurements are [B99-W58-H90 cm] [B39-W23-H35 in]. Her body weight is [58 kg] [128 lbs].

Her most distinctive feature is her long, beautiful crimson hair, which she also inherited from her father, that reaches down to her thighs with a single hair strand (known in Japan as ahoge) sticking out from the top. Her hair also has loose bangs covering her forehead and side bangs framing her face. Rias' height is 172 cm. (5 feet 8 inches), making her one of the tallest female characters of the series. As a Devil from the House of Gremory[2], Rias is very kind and compassionate, especially to her servants and people close to her. She gets angry and violent whenever people insult her or her peerage, showing a fiery side to her.