Who is this?
Dame Agatha Mary Clarissa Christie, Lady Mallowan, DBE (15 September 1890 – 12 January 1976) was an English crime novelist, short story writer and playwright. She also wrote six romances under the name Mary Westmacott, but she is best known for the 66 detective novels and 14 short story collections that she wrote under her own name, most of which revolve around the investigative work of such characters as Hercule Poirot, Jane Marple, Parker Pyne, Harley Quin/Mr Satterthwaite and Tommy and Tuppence Beresford. She wrote the world's longest-running play, a murder mystery, The Mousetrap.
And here is a very nice bio piece on Christie that includes the above photo: Agatha Christie