Thomas F. Eagleton, a three-term Democratic senator from Missouri who resigned as George McGovern's vice presidential nominee in 1972 after it was revealed he had been hospitalized for depression, died Sunday in St. Louis, said a spokeswoman for Sen. Claire McCaskill, D-Mo.

Eagleton, 77, had suffered from a variety of illnesses and ailments in recent years. A cause of death was not disclosed.

"Today Missouri has a hole in its heart," McCaskill said in a statement. "Tom Eagleton managed to be a statesman, an intellectual and a man of the people all at the same time.

"At many times in his career he demonstated both political and personal courage," McCaskill said. "He will be an important part of history for generations to come. Along with his legions of friends and colleagues, I'm devastated."

Former Sen. John Danforth of St. Louis, a Republican, served alongside Eagleton for 10 years and was his friend for four decades, despite their political differences. Danforth was traveling Sunday, but said in a statement that Eagleton's death was a great loss to the state and to him personally.

"Tom Eagleton was an outstanding public servant throughout his career in elective politics and beyond," Danforth said. "As a United States senator, he was highly respected on both sides of the aisle. He was a person of high principle and consistent good humor."

Sen. Kit Bond, R-Mo., said Eagleton "cared deeply about Missouri and its citizens. His long career in public service is a power example to all of us that we are here to make a difference and should dedicate ourselves to causes larger than ourselves."

Eagleton was born in St. Louis in 1929, the son of noted civil trial attorney Mark Eagleton, who once ran unsuccessfully for mayor and encouraged his son's interest in politics. He was elected circuit attorney at age 26 in 1956, just three years after graduating from Harvard Law School. He was the youngest man ever elected to the position.

He was elected Missouri attorney general in 1960 and lieutenant governor in 1964 before winning election to the U.S. Senate in 1968. He won re-election in 1974 and 1980, retiring after his third term.

After McGovern chose the 42-year-old senator as his running mate, it was soon learned that Eagleton had suffered from depression and undergone shock treatments a decade earlier.

After initially vowing to back Eagleton "1,000 percent," McGovern eventually chose Sargent Shriver, an in-law of the Kennedys, to replace Eagleton. Richard Nixon trounced McGovern to win re-election.

"My personal feelings are secondary to the necessity to unify the Democratic Party and to elect George McGovern as the next president of the United States," Eagleton said at the time.

Eagleton remained in the Senate until 1987, serving on the Appropriations, Governmental Affairs, Ethics and Foreign Affairs committees. Generally considered liberal, he nevertheless criticized busing to achieve school desegregation and, as a practicing Roman Catholic, strongly opposed abortion.

Eagleton told The Associated Press in 2003 that he had no regrets.

"Being vice president ain't all that much," he said. "My ambition, since my senior year in high school, was to be a senator. Not everybody achieves their ambition. I got to the level that I really had no great right to claim."

Eagleton was sixth on McGovern's initial list of prospective running mates. Higher-ranked choices, including Massachusetts Sen. Edward Kennedy, either turned down McGovern's offer or were ruled out.

Eagleton was interviewed over the phone by McGovern aide Frank Mankiewicz on July 13, 1972, and quickly agreed to join the ticket.

Eagleton recalled in the interview with AP that he was asked if he ever used drugs or drank excessively. The subject of mental illness didn't come up, and Eagleton said it didn't occur to him to mention his three hospitalizations during the early 1960s for "nervous exhaustion and fatigue."

He said he had not had any symptoms of depression for years and "didn't think it was all that big a deal."

But the stigma of mental illness proved troubling. Rumors quickly spread, prompting a joint news conference with Eagleton and McGovern.

"I am 1,000 percent for Tom Eagleton, and I have no intention of dropping him from the ticket," McGovern said. But six days later, with his backers deserting him, Eagleton stepped down.

The McGovern-Shriver ticket was badly beaten in November 1972, with Nixon and Vice President Spiro Agnew receiving 61 percent of the vote and carrying every state except Massachusetts.

"McGovern has said more than once, not always in my presence but sometimes, he thinks that's the biggest mistake he made in the campaign," Eagleton told the AP in 2003. "He thinks he would have done a lot better if he had left Eagleton on the ticket. Well, who knows?"

The two men remained friends, often chatting on the phone and writing. McGovern stayed at Eagleton's home a few years ago and the two attended a St. Louis Cardinals game.

Meanwhile, Eagleton said he "got over the disappointment damned quick," and threw himself into his Senate work.

He won a second term in 1974 by a lopsided majority. The 1980 race was much closer, when he defeated St. Louis County Executive Gene McNary by 89,460 votes out of more than 2 million ballots cast.

After he retired from the Senate in January 1987, Eagleton returned to St. Louis where he practiced law, taught at Washington University and did work as a television political commentator and occasional newspaper contributor.

He was also an activist for St. Louis, playing a key role in luring the NFL's Rams to relocate from Los Angeles in 1995, chairing the fan group that secured financing for the move. The federal courthouse in St. Louis is named after him.

Most recently, he was co-chairman for the Missouri Coalition for Lifesaving Cures, which backed a successful constitutional amendment in November guaranteeing that all federally allowed stem cell research also can occur in Missouri.

Significant hearing loss curtailed some of Eagleton's activities, but he was sought out by younger Democrats seeking advice and encouragement. Among his proteges was former Rep. Dick Gephardt.

Eagleton is survived by his wife, Barbara Ann Smith Eagleton, whom he married in 1956, and two children, son Terence and daughter Christin.