Garth Nix ( Set of 4 Books) Abhorsen, Across the Wall, Sabriel, Lirael.

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."