Jimmy Carter
Carter went to the opening ceremonies of his presidential library and those of Presidents Ronald Reagan, George H. W. Bush, Bill Clinton, and George W. Bush. He gave eulogies at the funerals of Coretta Scott King Gerald Ford, Theodore Hesburgh, and John Lewis. He has gone to the state funeral of every former president since he left office: Nixon in 1994, Reagan in 2004, Ford in 2006 and Bush Sr. in 2018. When going to the inauguration of Donald Trump in 2017, he became the oldest former president to go to one.