Former Senate Majority Leader Howard Baker, a Republican who reshaped Tennessee politics and was once thought to be a contender for the presidency, has died, his law firm said Thursday.

Baker, 88, served 18 years in the U.S. Senate. In 1966, he was the first Republican to be popularly elected to the Senate from Tennessee. Baker was also a chief of staff to President Ronald Reagan and a U.S. Ambassador to Japan.

In 1984, he received the Presidential Medal of Freedom, the nation’s highest civilian honor.

Baker had been in ailing health in recent years, but many Tennessee Republicans hail him as one of the most important figures in their party’s history.

“Howard Baker was Tennessee’s favorite son, one of America’s finest leaders and for Honey and me an indispensable friend,” U.S. Sen. Lamar Alexander said in a statement. “He built our state’s two-party political system and inspired three generations to try to build a better state and country. It is difficult to express how much we honor his life and how much we will miss him.