Thomas Leo Clancy Jr. (born April 12, 1947) is an American author, best known for his technically detailed espionage and military science storylines set during and in the aftermath of the Cold War and his video games. His name is also a brand for similar movie scripts written by ghost writers and many series of non-fiction books on military subjects and merged biographies of key leaders. He is also part-owner of the Baltimore Orioles, a Major League Baseball team. He officially is the Orioles' Vice Chairman of Community Activities and Public Affairs.

Thomas Leo Clancy, Jr. was born in Annapolis, Maryland, United States. He attended Loyola Blakefield in Towson, Maryland, graduating with the class of 1965. He studied English Literature at Loyola College in Baltimore, graduating in 1969. Though he wanted to serve in the United States military, he was rejected after failing a required eye exam in the ROTC. Before making his literary debut, he spent some time running an independent insurance agency.

In 1993, Tom Clancy joined a group of investors that included Peter Angelos and bought the Baltimore Orioles from Eli Jacobs. In 1998, he reached an agreement to purchase the Minnesota Vikings, but had to abandon the deal due to the cost of his divorce settlement.