Cleo is a magician from Rio de Janeiro. She is currently studying magic under the Kane siblings at Brooklyn House and is in charge of their library, being an avid reader. She wants to follow the path of Thoth. She takes cares of the scrolls, artifacts, and shabti in the library. Sadie and Carter depend on her to locate scrolls, artifacts or statues that they need.
She participated in the Battle of Brooklyn House, chanting incantations such as "Blind!", "Horizontal!", and "Gassy!" at the attackers. She is described as a bookworm but her actions in the Battle of Brooklyn House prove she is just as brave as the others.
Cleo acts as Brooklyn House's self-appointed librarian and is good at it. She notes a pattern in Apophis' attacks on various Nomes: they all have one of six copies of the Book of Overcoming Apophis written by Setne in them. Thanks to her information, they are able to track the last copy to the Dallas Museum and though they fail to get the book, they find a clue to defeating Apophis. Cleo is later saddened to hear about the destruction of the Fifty-First Nome and is kicked out the library so the Kanes and Bast can talk privately.
Cleo takes part in the Battle of the Hall of Ages despite her aversion to fighting and defeats a rebel magician, turning him into a human-sized version of the novel David Copperfield. She gets one of her arms turned into a sunflower, but Jaz heals her of the injury. She takes part in the final battle and survives.
Cleo has no stomach for battle. Sometimes she seems to prefer books to her real life. Despite this, she can be brave when necessary as shown during the Battle of Brooklyn House and the Battle of the Hall of Ages and can hold her own. She maintains and constantly organizes the library at Brooklyn House (with help from the shabti). She has a strong relationship with Khufu, the baboon. Cleo also has a great hunger for information and for organizing it, like her patron, Thoth. This is evidenced when she began cataloging the entire Brooklyn House library.
Cleo is a powerful magician. However, she has no stomach for battle. During the battle of the First Nome, Cleo got in a duel with an enemy magician resulting in her arm being turned to a flower, while her opponent was turned into a book.
- Cleo's first language is Brazilian Portuguese. In moments of anxiety, she switches to her first language.
- She is the first main universe character from Brazil, the second being Paolo Montes.
- Cleo can speak multiple languages, including Ancient Egyptian, Portuguese, Baboon etc.