Who is Bertha in the book Jane Eyre?

Bessie was nurse at Mrs. Reed's house, she took care of Jane when was a child. Bessie was far more then a nurse to Jane, she was like Jane's mother. Charlotte Bronte has given a good character to Bessie, as Jane as the narrator recalls her as follows, "Bessie Lee must, I think, have been a girl of good natural capacity, for she was smart in all she did, and had a remarkable knack of narrative; so, at least, I judge from the impression made on me by her nursery tales. She was pretty too, if my recollections of her face and person are correct. I remember her as a slim young woman, with black hair, dark eyes, very nice features, and good, clear complexion; but she had a capricious and hasty temper, and indifferent ideas of principle or justice: still, such as she was, I preferred her to any one else at Gateshead Hall." (Page 20, Jane Eyre) This quotes shows that Jane liked Bessie more then anyone in Gateshead. She has a hasty temper and indifferent ides of principle or justice; I agree with this statement as she used to get very angry when Jane said anything rude to Mrs. Reed, although she never thought about the idea that Mrs. Reed was far more then rude to Jane. In the starting of the novel, it was clear that the minor character of Bessie was developed more then the character of Mrs. Reed.