The Terrorizers was the eighteenth novel in the Matt Helm secret agent novel series by Donald Hamilton.
 It was first published in 1977.
 Following the publication of this book, Hamilton put his longtime character on hiatus; the next Matt Helm novel, "The Revengers", would not be published until 1982.
Henry and Cato is a novel by Iris Murdoch.
 Published in 1976, it was her eighteenth novel.
Dame Jean Iris Murdoch ( ; 15 July 1919 – 8 February 1999) was an Anglo-Irish novelist and philosopher, best known for her novels about good and evil, sexual relationships, morality, and the power of the unconscious.
 Her first published novel, "Under the Net", was selected in 1998 as one of Modern Library's 100 best English-language novels of the 20th century.
 In 1987, she was made a Dame Commander of the Order of the British Empire.
 Her books include "The Bell" (1958), "A Severed Head" (1961), "The Red and the Green" (1965), "The Nice and the Good" (1968), "The Black Prince" (1973), "Henry and Cato" (1976), "The Sea, the Sea" (1978, Booker Prize), "The Philosopher's Pupil" (1983), "The Good Apprentice" (1985), "The Book and the Brotherhood" (1987), "The Message to the Planet" (1989), and "The Green Knight" (1993).
 In 2008, "The Times" ranked Murdoch twelfth on a list of "The 50 greatest British writers since 1945".
Toward the End of Time is a novel by American writer John Updike, published in 1997.
 It is the author's eighteenth novel.
Mr. Monk Is Open For Business is the eighteenth novel based on the television series "Monk".
 It was published on June 3, 2014.
 Like the other novels, the story is narrated by Natalie Teeger, Monk's assistant.
 It is the third novel in the series to be written by Hy Conrad.
The Mind Readers is a crime novel by Margery Allingham, first published in 1965, in the United Kingdom by Chatto & Windus, London.
 It is the eighteenth novel in the Albert Campion series.
The Iciest Sin is a crime novel by H. R. F. Keating.
 It is the eighteenth novel in the Inspector Ghote series but the nineteenth book to be published as an anthology of short stories was released the year before.
Scales of Justice is a detective novel by Ngaio Marsh.
 it is the eighteenth novel to feature Roderick Alleyn, and was first published in 1955.
 The plot concerns the murder of Colonel Carterette, an enthusiastic fisherman in charge of publishing the controversial memoirs of the local baronet.
L'Argent ("Money") is the eighteenth novel in the Rougon-Macquart series by Émile Zola.
 It was serialized in the periodical "Gil Blas" beginning in November 1890 before being published in novel form by Charpentier et Fasquelle in March 1891.
Flight of the Hawk is the eighteenth novel in "World of Adventure" series by Gary Paulsen.
 It was published on April 6, 1998 by Random House.

Question: What was the nationality of the novelist whose eighteenth novel was published in 1976? 
Answer: Anglo-Irish