Thomas Leo Clancy Jr. was an American novelist. He is best known for his technically detailed espionage and military-science storylines set during and after the Cold War. Seventeen of his novels have been bestsellers and more than 100 million copies of his books have been sold. His name was also used on screenplays written by ghostwriters, nonfiction books on military subjects occasionally with co-authors, and video games. He was a part-owner of his hometown Major League Baseball team, the Baltimore Orioles, and vice-chairman of their community activities and public affairs committees.

Clancy was born on April 12, 1947, at Franklin Square Hospital in Baltimore, Maryland and grew up in the Northwood neighborhood in northeast Baltimore. The family was Irish-American. He was the second of three children to Thomas Leo Clancy (1918–1995), who worked for the United States Postal Service, and Catherine Mary Clancy (née Langan; 1918–2001), who worked in a store's credit department. He was a member of Troop 624 of the Boy Scouts of America. Clancy's siblings are Patrick and Margaret.

Clancy's first wife, Wanda Thomas King, was a nurse. They married in 1969 and had four children. The couple separated briefly in 1995, and they permanently separated in December 1996. Wanda Clancy filed for divorce in November 1997, which became final in January 1999. As part of the divorce, she and Clancy split his minority stake in the Baltimore Orioles.