She is 5'10 and has a fit frame. She has blonde hair and green eyes. Her robes are always presentable and clean (they look almost always new). Her face is soft, yet her stare is strict and cold.
Cleo was born into a pure-blood family. She has a sister. She was admitted to Hogwarts in 2027 at age 11. She was sorted into Ravenclaw and did her best to earn Ravenclaw points and help them win the house cup. During her stay, she worked for the Quill and wrote articles regarding spells and Potions. She excelled in Charms, Potions, and Herbology. She did fairly well in Defense against the Dark Arts and did average to poorly in the other subject matters that held no interest to her.
After graduating from Hogwarts in 2034, she went to work for the Ministry as an Auror. In this position, she focused and slowly became specialized in the arts of potion-making and the use of herbs and plants. This specialization help her transition into a new position in the Department of Misteries as an Unspeakable. In such position, she exhaustively researched poisons, plants, and herbs in both worlds (muggle and wizard).
After working long years for the Ministry, she was offered a position to teach at Hogwarts, which she gladly accepted.
Cleo's behavior is usually seen as strict and demanding. She always expects the worst to happen and thinks that an exhaustive knowledge on the environment will help students survive. She is very cautious about things that are offered to her (for she knows all the different poisons and ways to sneakily attack an opponent or potential problem). She is also seen as being nice enough and appears to be carefully observing everyone around her.