These are doll-related characters that have been created by various doll companies or writers through the years, or that may even be based on real people. Doll company characters, like Addy from American Girl, often have books or movies made about them and have many products that bring the character's world to life. Other characters, like Cinderella or Madeline, were not created to be dolls but have had dolls created for them by many manufacturers over the years.
Use the "Add character" link to create a new character in this database. Note that custom characters from your own imagination should not be added here, but over in the Collection Tracker > My Custom Characters section.