Jon Ossoff

Senator Jon Ossoff of Georgia, the youngest member of the Senate and a rising star in the Democratic Party, is running unopposed in his party’s primary on Tuesday. His general-election race is one of several at the center of the battle for the Senate majority.

Here are five things to know about Mr. Ossoff, 39, of Atlanta.

1. He unseated an incumbent Republican in 2021. Mr. Ossoff defeated Senator David Perdue, a one-term Republican, in a runoff that year. The victory, which came by about a percentage point, helped Democratswin the Senate . It came as the Rev. Raphael Warnock, a Democrat, defeated Senator Kelly Loeffler, a Republican, giving Democrats both Senate seats in Georgia and propelling the party into the Senate majority.

2. He was the youngest politician to reach the Senate in decades. Mr. Ossoff was 33 when he was elected in 2021. His first run for office had been a losing but competitive campaign for the House in 2017 that drew national attention (He initially ran the congressional campaign out of his basement). He was the youngest person elected to the Senate since Don Nickles, an Oklahoma Republican, won his first term in 1980, at age 31. And Mr. Ossoff was the youngest Democrat to achieve the feat since Joseph R. Biden Jr. won his first term in the Senate in 1972. Mr. Biden was 29.