The Hungarian-born novelist Emma Magdalena Rosalia Maria Josefa Orczy is best known as the Baroness Orczy, the author of the Wordcandy classic The Scarlet Pimpernel.
Orczy began her career as an author of detective stories, and although many of her mystery series were popular (particularly "The Old Man in the Corner" books, which are considered to be the first "armchair detective" stories), none of them have had the enduring appeal of The Scarlet Pimpernel. Written in 1903, The Scarlet Pimpernel was rejected by over a dozen publishers, and it wasn't until Orczy and her husband (Montague Barstow) co-wrote a successful stage adaptation that the book found a publisher. Since the book is AWESOME, it didn't take long for wild success to come a-knockin', and Orczy eventually published fifteen (inferior) sequels.
Note: It's pronounced "Ort-zee", in case you were wondering.
Note #2: One of Jack the Ripper's victims was killed just outside the Baroness's London home in 1888.
Note #3: The Baroness was the daughter of the composer Baron Felix Orczy.
Availability: Everywhere for The Scarlet Pimpernel, libraries for her detective stories. There is also a Dover Thrift version of The Scarlet Pimpernel, so you have no excuse not to own it.