Ronald Reagan leaves behind many legacies, but among his most significant is a profound impact on American politics. Through the force of his convictions, his genial personality and his buoyant optimism, Reagan reshaped the Republican Party in his conservative image and with it transformed the politics of his country.

When he first appeared on the national political stage, Reagan was a speechmaker for Barry Goldwater in the closing weeks of the 1964 presidential campaign, an election that brought the worst drubbing for the GOP in the postwar era but also marked the birth of the modern Republican Party.

At the time of Reagan's Oct. 27, 1964, speech, the Republicans were in the minority and in the throes of a brutal battle pitting the long-dominant moderate eastern wing of the party against an emerging, conservative, grass-roots army of activists in the Sun Belt. By the time of Reagan's death, the two parties were at rough parity in support, but Republicans controlled the presidency, both houses of Congress and a majority of governorships. Beyond that, Reagan indelibly stamped his conservative image on economic policy, devoted to cutting taxes and reining in the domestic side of the federal government. He left a party dominated by the South and the West, its moderate wing nearly a distant memory and the rest united behind his belief in limiting the central government and projecting its military strength abroad. He left a party where conservatism on social issues is now the rule.

In the course of those years, the nation saw the breakup of both the Soviet Union and the Democratic coalition that Franklin D. Roosevelt assembled with the New Deal and World War II -- a coalition that included a young Ronald Reagan.

"Reagan was an FDR Democrat who understood being a majority and understood being optimistic and understood being positive," former House speaker Newt Gingrich said last night. "He brought those sentiments into a Republican Party that was really not thinking like or behaving like a majority party prior to Reagan."

Reagan served two terms as governor of California, his first election made possible by Richard M. Nixon's gubernatorial loss in 1962 and the network of Goldwater activists left over from the 1964 campaign. But when he finished there in 1975, he was still seen by many political analysts, and most Democrats, as a politician whose conservatism was outside the American mainstream.

He left the statehouse in Sacramento a month after Nixon resigned the presidency in disgrace after the Watergate scandal, with the national Republican Party in disarray. By early 1975, just 18 percent of Americans identified with the GOP, according to an account in "Governor Reagan," by his biographer, Lou Cannon.

Reagan then had the audacity to challenge a sitting Republican president by entering the 1976 GOP primaries against Gerald R. Ford, who had succeeded Nixon. In the opening months of the campaign, he suffered a string of defeats in primaries across the country, then turned his efforts around with a ferocious attack on Ford's foreign policy and its chief architect, Secretary of State Henry A. Kissinger, charging that Ford was giving away the Panama Canal. "We bought it, we paid for it, it's ours, and we're going to keep it," he said.

Reagan struck a chord in North Carolina, and his primary victory there revived his campaign. A victory in the Texas primary soon after gave him the momentum to battle his way to the Republican convention in Kansas City, Mo., where he and Ford engaged in trench warfare over the remaining unpledged delegates.

Ford won the battle and thus the nomination, but Reagan won the war. With Ford's loss to Jimmy Carter that November, Reagan emerged as the dominant figure in the party leading a revitalized conservative movement. The nomination was his to lose in 1980.

Reagan's 1980 campaign symbolized the emergence of the conservatives as the dominant force in the party 16 years after the Goldwater debacle, and Reagan owed much to the intellectual and ideological foundation laid by the Arizona senator in that losing cause. "Nixon was the old establishment, and Reagan picked up the conservative mantle from Goldwater and had a better ability to communicate the message," said Ed Rollins, who managed Reagan's 1984 campaign.

What the 1980 campaign demonstrated, to the surprise of many Democrats who underestimated his political skills, was Reagan's ability to enunciate strong conservative principles without being threatening to a majority of Americans. With Carter weighed down by an economy plagued by rising oil prices and inflation out of control and a hostage crisis in Iran that continued throughout the year, Reagan exploited the country's demoralized mood with an upbeat campaign in which he promised to return the country to greatness.

That campaign marked a major shift in the Republican Party's approach to economics when he embraced the supply-side tax-cutting philosophy of many young conservatives. The man he eventually would choose as his vice president, George H.W. Bush, dubbed it "voodoo economics" during their battle for the nomination, and John B. Anderson, who started the campaign as a Republican but left the party to run an independent candidacy, said Reagan's promises to cut taxes, boost the defense budget and balance the budget amounted to "blue smoke and mirrors."

The principles that undergirded Reagan's campaign to the White House guided his actions as president, as he pushed his party and the country farther to the right. Despite criticism from mainstream economists, Reagan sought and won a major tax cut in his first year in office as well as a budget plan designed to reduce the size of the federal government.

Although he was forced later in his term to raise taxes to offset some of the revenue lost from that 1981 measure, and though he never achieved the kind of spending cuts he liked to talk about, the principles of cutting taxes and limiting the size of government were embedded in mainstream Republican philosophy.

"Beginning with Roosevelt, the presumption was that if you had a problem, the federal government was going to solve it," said David Keene of the American Conservative Union. "Beginning with Reagan, the presumption was that if you had a problem, government was likely to screw things up and you looked for a private solution."

Reagan's presidency brought a new term to the political lexicon: Reagan Democrats. His social conservatism, his unapologetic appeals to patriotism, his challenge to the Soviets and his economic policies brought onetime Democrats streaming into the Republican column. He won reelection in a landslide in 1984 with his "morning in America" message, carrying 49 states against former vice president Walter F. Mondale, leaving the Democratic Party a shambles and in need of reform.

"Without Ronald Reagan, we would not have the shift in partisanship where the parties are virtually split," said Richard B. Wirthlin, who was Reagan's pollster. "The Democratic Party could have extended its dominance much longer without Reagan's appeal to blue-collar workers, some labor unions, the South and young people. Those were the four groups that moved most dramatically in 1980, and most of that shift has endured."

Reagan's second term was marred by the Iran-contra scandal, which badly damaged his administration and brought embarrassment to Reagan. His approval rating plummeted to 40 percent in January 1987, significantly tarnishing his image. But the second term also brought success in his overriding foreign policy objective, which was challenging the Soviet Union. From "evil empire" to "Mr. Gorbachev, tear down this wall," he never shrank from confrontation, but eventually his ideology gave way to pragmatism and negotiation. His policies helped hasten the breakup of the Soviet Union and eventually the end of the Cold War.

Reagan's presidency inspired a generation of Republican politicians, from the Gingrich generation who began as House backbenchers during his presidency and eventually drove the revolution that resulted in a Republican takeover of Congress in 1994, to George W. Bush, whose 2000 presidential campaign bore many more elements of Reagan's politics that those of his father.

As Grover Norquist, president of Americans for Tax Reform, put it last night: "George W. Bush has governed as if it were the third term of Ronald Reagan's presidency. People who are looking to run for president in 2008 will run as Ronald Reagan's heirs."

"It is undeniable," said Ralph Reed, former chairman of the Georgia GOP, "that the Republican Party of today is largely the party that he remade -- a conservative party, a grass-roots party, and one whose candidates, with very few exceptions, pledge fealty to the principles that he articulated."

Reagan's political success also forced Democrats to undergo their own transformation, led by Bill Clinton in his 1992 campaign. Democrats under Clinton sought to shed their image as tax-and-spend liberals and as a party whose foreign policy was paralyzed by its opposition to the Vietnam War. In shifting the party to the center, Clinton challenged the rise of the Republicans and helped produce the parity between the parties that exists today.

Reagan's political career was marked by strategic retreats from his stirring conservative rhetoric, pragmatism when he needed it, and a number of instances where he failed to come close to achieving his goals, most notably in bringing the federal deficit under control. But in the almost 16 years since he left the presidency to return to California, his influence on the party and the politics of the country has never waned. Few politicians in the history of the country have had that kind of lasting legacy.

Researcher Lucy Shackelford contributed to this report.

In September 1990, four years after he stood at the Berlin Wall and urged that it be torn down, former president Reagan visited a reunited Germany and chipped away at one of the last remnants of the barrier, near the Brandenburg Gate.