John Hardy Isakson (December 28, 1944 – December 19, 2021) was an American businessman and politician who served as a United States senator from Georgia from 2005 until his resignation in 2019 following health concerns. A member of the Republican Party, he previously served in the Georgia legislature and the United States House of Representatives.

Born in Atlanta, Georgia, Isakson served in the Georgia Air National Guard (1966–1972) and graduated from the University of Georgia. He opened a real estate branch for Northside Realty and later served 22 years as the company's president. After a failed bid for the Georgia House of Representatives in 1974, he was elected in 1976. He served seven terms, including four as minority leader. Isakson was the Republican candidate for governor of Georgia in 1990, but lost. Two years later, he was elected to the Georgia Senate and served one term. He unsuccessfully ran in the Republican primary in the 1996 U.S. Senate election.

After 6th District Congressman and Speaker of the House Newt Gingrich resigned, Isakson ran in the February 1999 special election to succeed him, winning by a 40-point margin. He ran for the U.S. Senate in 2004 after Democratic incumbent Zell Miller opted not to run for re-election. With the backing of much of Georgia's Republican establishment, he won both the primary and general elections by wide margins. He became the senior senator from Georgia when Saxby Chambliss retired in 2015. On December 31, 2019, midway through his third Senate term, Isakson resigned from the Senate due to health concerns and was succeeded by fellow Republican Kelly Loeffler who was appointed by Brian Kemp, the Republican Governor of Georgia, to fill the vacant seat. He died two years later on December 19, 2021.

Isakson was born on December 28, 1944, in Atlanta, Georgia, the son of Julia (née Baker) and Edwin Andrew Isakson, a Greyhound bus driver, who later established an Atlanta real estate firm. His paternal grandparents were of Swedish descent, and his paternal grandfather was born in Östersund. His mother was of mostly British ancestry, and her family has been in the American South since the colonial era.

Isakson served in the Georgia Air National Guard from 1966 to 1972, leaving service as a staff sergeant. Isakson enrolled at the University of Georgia, where he became a member of the Sigma Alpha Epsilon social fraternity. Shortly after graduating from UGA, he opened the first Cobb County office of Northside Realty, a prominent Atlanta-area real estate firm that his father, Ed, helped to establish. Isakson became company president in 1979, a post he held for 22 years, during which Northside became the biggest independent real estate company in the Southeast and one of the largest in the United States.^{[better source needed]}

In 1974, Isakson first ran for the Georgia House of Representatives in an eastern Cobb County district and lost. He ran again in 1976 and won. He served seven terms in the House. He won re-election unopposed in 1984 and 1988. In his last four terms (1983–1990), he was the Republican Minority leader. In 1988 and 1996, he was co-chair for U.S. Senator Bob Dole's presidential primary campaigns.

Isakson was the Republican candidate for Governor of Georgia in 1990. He won the Republican primary with 74% of the vote in a four candidate field. In the general election, he was defeated by Democratic Lieutenant Governor Zell Miller 53%–45%. His campaign was managed by Jay Morgan while Miller's campaign was managed by James Carville. Miller ran on a pledge to start a state lottery and use the revenue for public schools. Isakson proposed a ballot referendum on the lottery.

In 1992, Isakson was elected to the Georgia Senate.