Founder of Ravenclaw House and one of the co-founders of Hogwarts, described with the other founders as “the greatest wizards and witches of the age.” According to Jo’s website, Ravenclaw was “the most brilliant witch of her time” (JKR). She prized the students whose intelligence was surest (OP11, FW), and had the motto, “Wit beyond measure is man’s greatest treasure.” (DH)
Rowena Ravenclaw had a fraught relationship with her daughter, Helena. Helena was jealous of her mother’s renown, and stole Ravenclaw’s prized diadem. Rowena was ashamed of this, and concealed it from everyone, even the other founders (DH31). When Rowena fell fatally ill, she attempted to get her daughter back for a reconciliation by sending the Bloody Baron after her, and Helena was killed as a result. Rowena Ravenclaw never recovered her diadem, and emotionally never recovered from her daughter’s betrayal. While the facts became obscured by time, it became part of her legend that she died of a broken heart (JKR).
According to the Sorting Hat, Ravenclaw came “from glen,” which probably means somewhere in Scotland, such as Glencoe or the Great Glen where Loch Ness is.
Her Famous Wizard card tells us that "[i]t's thought that she came up with the ever-changing floor plan. She's best remembered for her intelligence and creativity."