Rowena Ravenclaw is a fictional character from the Harry Potter Universe. She is known as being one of the four founders of Hogwarts. She is also known as the posessor of the Diadem of Ravenclaw (or The Lost Diadem), which was taken by Voldemort and was overthrown by dark magic, a powerful tiara which enhances the wisdom of its wearer. Ravenclaw House was named after her, and she preferred the students who were more "wise" and interested in their studies. She had the house Ravenclaw named after her, as she was one of the four founders of Hogwarts.
It is likely that Rowena, was brought up as a Half-blood, because she went againstSalazar Slytherin when he wanted only pure-bloods in the school.