Some debate exists over the identity of Beloved. While some critics claim that she is the spirit of Sethe's murdered daughter, others argue that she is a human woman who is mentally unstable. The most common interpretation of the Beloved character, however, is that she is the spirit of Sethe's dead child and, as Denver notes, "something more." That something more is a collective spirit of all the unnamed slaves who were torn from their homes in Africa and brought to America in the cramped and unsanitary holds of slave ships. You can find evidence for this interpretation in Beloved's stream of consciousness narrative in Chapter 22. In this chapter, Beloved remembers crouching in a hot place where people are crowded together and dying of thirst.
Because Sethe's mother came from Africa, the experience that Beloved remembers is also Sethe's mother's experience. In a sense, Beloved is not only Sethe's daughter but her mother as well. Because Beloved is supernatural and represents the spirit of multiple people, Morrison doesn't develop her character as an individual. Beloved acts as a force rather than as a person, compelling Sethe, Denver, and Paul D to behave in certain ways. Beloved defines herself through Sethe's experiences and actions, and in the beginning, she acts as a somewhat positive force, helping Sethe face the past by repeatedly asking her to tell stories about her life. In the end, however, Beloved's need becomes overwhelming and her attachment to Sethe becomes destructive.
Notice that Morrison dedicates the book to "sixty Million and more," an estimated number of people who died in slavery. Beloved represents Sethe's unnamed child but also the unnamed masses that died and were forgotten. With this book, Morrison states that they are beloved as well.