Frederick William Nolan (born 7 March 1931 in Liverpool) is an English editor and writer, mostly known as Frederick Nolan, but also using the pen names Donald Severn, Daniel Rockfern, Christine McGuire and Frederick H. Christian.

He was educated in Liverpool and Aberaeron, Wales. At the age of twenty one, he began the researches that established him as one of England's leading authorities on the American West. In 1954 he was co-founder of The English Westerners' Society.

At the start of his career, he became first a reader, and later an editor, for Corgi (Bantam) Books in London. The move to London in the early Sixties made it possible for him to pursue the other consuming interest of his life: the American musical theatre. During this time, he also began writing western fiction as Frederick H. Christian, a pseudonym derived from his own, his wife Heidi's, and his oldest son's first names.

Over the next decade, while working in publishing - with Transworld, then Penguin, Collins, and Granada in London, and later with Ballantine and Warner in New York, he produced fourteen westerns as well as a considerable body of journalism.

On July 4, 1973, Nolan made his own "declaration of independence", quit his job as a highly paid publishing executive and signed a contract to write eight full length novels in a year. The first of these was the hugely successful The Oshawa Project (published in the US as The Algonquin Project) which was later filmed by MGM as Brass Target, starring Sophia Loren, John Cassavetes, Robert Vaughn, George Kennedy, Patrick McGoohan and Max von Sydow. Since that time he has completed over seventy books, not to mention as many biographical studies and articles for historical journals.

Considered to be one of the foremost authorities on the life and times of Billy the Kid, and the history of the American West in general, he appears frequently in TV documentaries dealing with the subject, as well as lecturing to historical societies in the UK and US, and also on cruise ships.

His westerns included the Angel series of books, as well as five additional books in the Sudden series that had been created by Oliver Strange. These have latterly been reissued under new titles, while the Angel series now appears under the pseudonym Daniel Rockfern (which is an anagram of "Frederick Nolan").

In 1993 Frederick Nolan received the Border Regional Library Association of Texas’ Award for Literary Excellence. In 2001 he was awarded the first France V. Scholes Prize for outstanding research from the Historical Society of New Mexico and during the same year, he received the first J. Evetts Haley Fellowship from the Haley Memorial Library in Midland, Texas. In 2005 the Western Outlaw-Lawman History Association (WOLA) gave him its highest honour, the Glenn Shirley Award, for his lifetime contribution to outlaw-lawman history; in 2006 The Westerners Foundation named his The West of Billy the Kid as one of the 100 most important 20th-century historical works on the American West, and in 2007 the National Outlaw-Lawman Association (NOLA) awarded him its prestigious William D. Reynolds Award in Recognition of Outstanding Research and Writing in Western History. A year later, True West Magazine named him "Best Living Non-fiction Writer."