A. J. Quinnell was the pen name of the English thriller novelist Philip Nicholson. He is best known for his novel Man on Fire, which has been adapted to film twice, most recently in 2004 featuring Denzel Washington.

Nicholson traveled throughout his life and several of the minor characters in his books are based on real people that he encountered in his travels. Nicholson was married three times; his last wife, Elsebeth Egholm, is a Danish mystery novelist. The couple maintained residences on the island of Gozo and in Denmark.

When the author was preparing to publish his first book, Man on Fire, he wanted to keep his real identity a secret. During a conversation in a bar, his agent (who is also J. K. Rowling's agent) told him he could use a pseudonym.^{[citation needed]} The author chose "Quinnell" after rugby union player Derek Quinnell and "A. J." from the initials of the bartender's son.

The author's best-known creation was the character of Marcus Creasy, an American-born former member of the French Foreign Legion. The Creasy novels are cult favorites in Japan.