The Reverend Jerry Falwell, a leading US conservative evangelist, has died in hospital in Virginia after being found unconscious in his office.
Doctors gave Mr Falwell emergency treatment at Lynchburg General Hospital but could not revive him.
US President George W Bush paid tribute to Mr Falwell, 73, who he said lived a life of "faith, family, and freedom".
Mr Falwell, who founded the Moral Majority movement in the 1970s, had a history of heart problems.
He rose to prominence after founding Liberty University, a conservative educational establishment in his home town of Lynchburg, Virginia, in 1971.
Mr Falwell was regarded as the father of the political evangelical movement.
As one of the first television preachers, he reached millions on his programme The Old Time Gospel Hour.
President Bush said both he and his wife, Laura, were "deeply saddened" by Mr Falwell's death.
"He taught young people to remain true to their convictions and rely upon God's word throughout each stage of their lives," Mr Bush said.
Ron Godwin, executive vice-president for Liberty University, said Mr Falwell was found unresponsive in his office at about 1045 local time (1545 GMT) after missing an appointment.
Mr Godwin said: "Dr Falwell is a huge, huge leader here in this area and in the nation at large."
The Reverend Al Sharpton said he was saddened and was praying for the Falwell family. He said although he often disagreed with the reverend, they had a cordial relationship.
The BBC's Vanessa Heaney in Washington says Mr Falwell was a controversial figure who offended many.
But his alliance with Republicans in the 1980s was a key help in the elections of Ronald Reagan as president and many political leaders have since continued to seek his support.
Among them is Senator John McCain - a Republican contender for US president - who described him as "a man of distinguished accomplishment who devoted his life to serving his faith and country".
Mr Falwell was a strong opponent of abortion, homosexuality and many other issues that conflicted with his fundamentalist Christian beliefs.
His statements on feminism and race issues often outraged liberals.
In 2002, he sparked anger across the Muslim world by calling the Prophet Muhammad a "terrorist". He later apologised.
Shortly after the 11 September 2001 attacks, he said that gays, atheists, civil-rights activists and legal abortions in the US had angered God and "helped this happen".
In 1999, he denounced the BBC TV children's show The Teletubbies, because he believed one character, Tinky Winky, was homosexual.