Percy Jackson and the Olympians: Legends

Ratatoskr himself appears as an abnormally large squirrel with anthropomorphic traits, such as a more humanoid face. He is missing his left eye and wears clothing and pauldrons. His spectral counterparts appear the same size and shape as normal squirrels, albeit with a ghostly figure.

Ratastoskr is humble, polite and kind and never insults anyone, and always refers to people as "Master", as a form of politeness. Ratatoskr has shown true loyalty and genuine care towards his associates. He is also quite understanding and grateful. However, as he has the power to remove aspects of his personality that he finds distracting, negative emotions are still considered to be part of his personality. He could show anger and frustration. He has shown to be possessive of the World Tree.

According to Ratatoskr, he was originally just a normal squirrel who almost died to a predator, but as he arrived on the World Tree, the World Tree saw potential in him and made him Yggdrasil's tenant, giving him the responsibility of overlooking the Nine Realms and ensuring their status as well as tending to the World Tree, fulfilling its needs. He had a working relationship with Níðhögg, who had tended to the World Tree long before him, and eventually removed aspects of his personality that he found disturbing so he could focus more on the World Tree. This also allowed Ratatoskr to sense events happening in the Nine Realms, granting him sight over it to compensate for his inability to leave the World Tree and making him able to be prepared whenever occurrences in a Realm requires his interference. Previously, He attacked Magnus, Blitzen, and Hearthstone in Hotel Valhalla when the latter duo climbed Yggdrasil to get to Valhalla. He was very strong, but was pushed back.