Former Indiana Sen. Birch Bayh (D) died Thursday at the age of 91 from pneumonia, his family announced.

Bayh, the father of former Sen. Evan Bayh (D-Ind.), served three terms in the Senate. He died Thursday morning at his home in Easton, Md., according to The Washington Post.

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“He had a natural sympathy for the underdog and the downtrodden. So that’s why he always tried to champion opportunity and decency for people who are born without a lot of either,” Evan Bayh told the Indy Star.

“My father was an extrovert who was devoted to his fellow citizens and trying to make their lives better — and he succeeded. And I can’t imagine a better legacy," he added.

Before serving in the Senate, Birch Bayh served four terms as a member of the U.S. House. He would later go on to run for president in 1976, with the Democratic nomination ultimately being secured by former President Carter.

Bayh authored two constitutional amendments during his time in Congress, one updating the line of succession following the assassination of President John F. Kennedy and another lowering the voting age to 18. He also worked on legislation establishing Title IX protections for women in higher education and authored the Equal Rights Amendment.

He left the Senate in 1980 following the election of former President Reagan, defeated by an energized Republican base that rallied around his opponent, Dan Quayle, who would later go on to become vice president.

"He amended the Constitution twice and forced open the doors of higher education opportunities to women, counseled presidents and met dozens of heads of state, even the pope," Bill Moreau, a former aide to the senator, told the Indy Star. "But he always thought of himself as the farm boy from Shirkieville who was the luckiest man on earth."