Isabella "Bella" Marie Cullen (née Swan), was born to Charlie Swan and Renée Dwyer on September 13, 1987, and is the main protagonist of the Twilight Saga. In Twilight, she is a 17-year-old girl who transfers schools from Phoenix, Arizona to Forks, Washington to live with her father Charlie, where she meets and falls in love with a vampire, Edward Cullen.

In Breaking Dawn, she marries Edward on August 13, 2006 and becomes a member of the Olympic coven. She is transformed into a vampire by Edward after nearly dying giving birth to their daughter, Renesmee Cullen, a human/vampire hybrid. Bella is the daughter-in-law of Edward, Sr. and Elizabeth Masen, as well as the adoptive daughter-in-law of Carlisle and Esme Cullen. She is the adoptive sister-in-law of Alice and Emmett Cullen, and of Jasper and Rosalie Hale.

As a human, Bella possessed a natural immunity to the mental powers of vampires. After her transformation into a vampire, she develops it into the ability to project a mental shield that protects others from the psychic powers of other vampires.