Passage: Years later in the present day, Carl still lives in the house by stubbornly holding out while the neighborhood homes are torn down and replaced by skyscrapers. When he accidentally injures a construction worker, the court deems him a public menace and orders him to move to a retirement home. However, Carl resolves to keep his promise to Ellie by turning his house into a makeshift airship using thousands of helium balloons. Russell, a young "Wilderness Explorer" who visits Carl in his effort to earn his final merit badge for assisting the elderly, becomes an accidental stowaway.

Question: Who promised Ellie?
Carl