Helen Ruth Castor FRSL (born 4 August 1968) is a British historian of the medieval and Tudor period and a BBC broadcaster.

She taught history at the University of Cambridge and is the author of books including Blood and Roses (2004) and She-Wolves: The Women Who Ruled England Before Elizabeth (2010).

[4][5] Castor was Director of Studies in History at Sidney Sussex College for eight years before focusing on writing and media.

[7] Castor's book Blood and Roses (2004) is a biography of the 15th-century Paston family, whose letters are the earliest-surviving collection of private correspondence in the English language.

[17] The judging panel of Castor, broadcaster Shahidha Bari, novelist and critic M. John Harrison, novelist and poet Alain Mabanckou, and cultural historian, writer, broadcaster and panel chair Neil MacGregor selected The Seven Moons of Maali Almeida by Shehan Karunatilaka.