Rachel Brown Oleson is the wife of Willie Oleson.
Rachel was the daughter-in-law of Harriet and Nels Oleson. Her family was poor but she was beautiful and kind and Willie fell in love with her. Harriet disliked Rachel very much saying her son was not going to marry a girl like Rachel and tried to stop them from getting married. (Episode 921: May I Have This Dance?) It was never spoken out loud but it seems Mrs. Oleson has stopped hating her.