Justice Antonin Scalia, a towering conservative voice on the US Supreme Court, has died at the age of 79, triggering a political showdown over his succession in the run-up to the presidential election.
President Barack Obama ordered flags to fly at half-staff across the United States until the long-serving justice, first appointed by Ronald Reagan in 1986, is laid to rest.
Scalia's death after three decades on the Supreme Court bench has profound ramifications, and could potentially tip the balance of the highest court in the land from its current 5-4 conservative majority to a liberal one.
Obama led the chorus of tributes pouring in for the stalwart conservative, who died in his sleep at a private residence in the Big Bend area of West Texas, according to the US Marshals Service.
"For almost 30 years, Justice Antonin Scalia was a larger than life presence on the bench, a brilliant legal mind with an energetic style," Obama told reporters in Rancho Mirage, California.
"Tonight we honor his extraordinary service to our nation and remember one of the towering legal figures of our time."
But the US leader also fired the first shot in a tense battle over Scalia's succession.
Obama said he fully intended to nominate a successor, in accordance with his "constitutional responsibilities," after leading Republicans -- including all six conservative White House contenders -- argued that the outgoing president should not be allowed to fill Scalia's vacant seat.
He called for the Republican-controlled Senate to give his nominee a "fair hearing and a timely vote."
"These are responsibilities that I take seriously as should everyone," Obama said. "They're bigger than any one party. They are about our democracy."
The president nominates a Supreme Court candidate, who requires Senate approval before taking up the lifetime post.
For three decades, Scalia's outsized personality gave voice to the values of conservative America on the Supreme Court bench, on matters of religion, family, patriotism and law enforcement.
A staunch defender of gun rights and the death penalty, the Roman Catholic justice was also openly opposed to abortion, gay marriage and affirmative action.
The Supreme Court's conservative majority had recently stalled key efforts by Obama's administration on climate change and immigration, and replacing Scalia with a Democratic appointee could significantly alter the balance of the court.
Republicans immediately drew battles lines over the implications of the vacancy.
"The American people should have a voice in the selection of their next Supreme Court Justice," said Senate Republican Majority Leader Mitch McConnell. "Therefore, this vacancy should not be filled until we have a new president."
Senator Chuck Grassley, Chairman of the Senate Judiciary Committee, also called for a delay.
"It's been standard practice over the last 80 years to not confirm Supreme Court nominees during a presidential election year," he said.
The Republican calls met with a sharp rebuttal from the Democratic camp.
McConnell's Democratic counterpart Harry Reid pressed for Obama to send a nominee to the Senate "right away," stressing that a yearlong vacancy -- raising the prospect of 4 to 4 splits on major issues -- would be "unprecedented."
"Failing to fill this vacancy would be a shameful abdication of one of the Senate's most essential Constitutional responsibilities," Reid said.
Democratic White House hopeful Hillary Clinton said Republicans calling for a delay "dishonor our Constitution."
The often belligerent Scalia, the first Italian-American to serve on the Supreme Court, was known for his brash demeanor and sharp tongue, his biting opinions making him a hero of conservatives and causing the ire of his liberal foes.
"War is war and it has never been the case that when you capture a combatant, you have to give them a jury trial in your civil courts," he once said, referring to prisoners at the US military prison at Guantanamo Bay. "It's a crazy idea to me."
Scalia was a champion of originalism, a strict theory that views the Constitution's meaning as fixed at the time it was ratified. According to this view, there is no doubt as to the validity of the death penalty and individuals' right to bear arms.
His affable personality and portly physique contrasted with his sometimes radical ideas -- and he was often the only justice on the otherwise stern bench to trigger a laugh in highly technical debates.
On the debate stage in South Carolina Saturday night, all six challengers for the Republican presidential nomination bowed their heads in silence to honor the late justice -- and united to oppose Obama nominating his successor.
Senator Marco Rubio warned Obama would seek to "ram down our throat a liberal justice."
"This is a tremendous blow to conservatism," Republican frontrunner Donald Trump warned of Scalia's death. He said he fully expects Obama to nominate a justice -- and said it was up to Republicans in the Senate to "delay, delay, delay."