Mattel produced Disney Princess dolls before Hasbro became the licensee in 2016.
Mattel held the Disney Princess doll license for many years and made dolls based on characters such as Cinderella, Snow White, Ariel, Belle, Jasmine, and Rapunzel. The products formed a major part of the broader Disney Princess merchandise program.
In 2016, Hasbro took over the master toy license for Disney Princess and Frozen products. That change is why older Disney Princess dolls are often associated with Mattel, while later releases may carry Hasbro branding.
The license concerned dolls and related toy products, not ownership of the Disney Princess characters. Disney retained the characters and brand; the toy company received permission to design, manufacture, and distribute licensed products.