Garth Nix (born 19 July 1963 in Melbourne) is an Australian author of young adult fantasy novels, most notably the Old Kingdom series, The Seventh Tower series, and The Keys to the Kingdom series. Garth Nix is not a pseudonym. He has frequently been asked this question and said, "I guess people ask me because it sounds like the perfect name for a writer of fantasy. However, it is my real name." His books are published around the world and have been translated into 36 languages. Nix's books have appeared on the bestseller lists of The New York Times, Publishers Weekly, The Bookseller, The Australian and The Sunday Times. http://en.wikipedia.org/wiki/Garth_Nix
Sabriel, 1996 CIP title page (Garth Nix)
www.theseventhtower.com, Jan. 8, 2001 (Garth Nix, b. 1963, grew up in Canberra)
Wikipedia, Mar. 26, 2013 (Australian author of young adult fantasy novels; born July 19, 1963; B.A., Professional Writing, University of Canberra, 1984-1986; continues to work in the publishing industry)