Like all lions, King Leonidas is arrogant. Even though he is not completely evil, he is sensitive and temperamental. Also, he possesses a deep love for the game of soccer, as seen when the royal championships on his Island could not continue when a suitable referee couldn't be found. He was extremely aggressive and roared at everything that moved.
He has an anti-human attitude, which may have stemmed from the fairy tale that animals staged a coup on the Isle of Naboombu, killing the original leader, the human wizard Astoroth. He wears the Star of Astoroth, a talisman that is needed to bring inanimate objects to life. After suffering much pummeling and stampeding at a soccer game, Mr. Brown succeeds in grabbing the Star of Astoroth from him. After being alerted by his secretary bird, an enraged Leonidas tries to pursue Mr. Brown, Miss Price, and the children, but he is foiled when he is turned into a rabbit, albeit one with a lion's tail, by Miss Price. He is last seen scurrying away. As Miss Price's rabbit spells are temporary, he presumably returned to his lion form soon after.