Mr. Clinton offered his tribute just moments after the announcement of Goldwater's death at age 89.
"He was truly an American original," the president commented. "I never knew anybody quite like him." He said that while he and Goldwater were from different political parties "and often different philosophies...he was uncommonly kind to me and to Hillary."
Mr. Clinton said he was a senior in college when he first met Goldwater and saw him from time to time, most recently just before the 1996 elections. "I always came away...with the impression that he was a great patriot and a truly fine human being."
The president said the nation's prayers would be with Goldwater's widow, Susan, and his family. "And our gratitude for his life of service to our country is very, very strong."
Sen. John McCain, who replaced Goldwater in the Senate in 1986, called his predecessor America's most ardent champion.
"America, the only nation ever founded in the name of liberty, never had a more ardent champion of liberty than Barry Goldwater. Simply put, Barry Goldwater was in love with freedom," said McCain, a Republican.
"Thank God that America had a Goldwater in its time. He was a great American," said retired Army Gen. Bill Quinn, a Goldwater friend of 35 years.
Goldwater biographer Jack Casserly said Goldwater, during their 34-year acquaintance, always had been "truthful, kind, courteous and, above all else, loyal.
"He was your friend forever, but if your opponent, an implacable foe. He never changed," Casserly said.
Former U.S. Sen. Paul Laxalt, R-Nev., praised Goldwater as "one of the giants of 20th century American politics."
Laxalt, a longtime friend and political and philosophical ally of Goldwater, said the Arizona senator "blazed the trail for the type of conservatism that has dominated government for the better part of three decades." He said the election of Ronald Reagan in 1980 would not have been possible without Goldwater's 1964 run.