Morwen Steelsheen was the wife of Thengel, the father of Théoden. They married in TA 2943 and had five children, including Théoden and Théodwyn (mother of Éomer and Éowyn). She was originally from Lossarnach in Gondor and she and her husband lived in Gondor for some time; their only son, Théoden was born in Gondor. Their last two daughters were born in Rohan after Thengel became king.
Morwen was 17 years younger than her husband, so she was probably born in TA 2922. She was called Steelsheen because of her grace and pride.