Former British Foreign Secretary Robin Cook (search), who quit Prime Minister Tony Blair's Cabinet in 2003 to protest the Iraq war, died Saturday after collapsing on a Scottish mountain while walking with his wife. He was 59.

Scotland's Northern Constabulary (search) said Cook collapsed on Ben Stack mountain in the Scottish Highlands. He was taken by coast guard helicopter to a hospital in Inverness, where he was pronounced dead.

Deputy Prime Minister John Prescott, filling in for a vacationing Blair, said Cook was "the greatest parliamentarian of his generation."

"He also made an enormous contribution to British politics in opposition and in government," Prescott said.

Michael Howard, leader of the main opposition Conservative Party (search), said Cook's political contribution had been "immense."

"He was a politician of principle who fought hard for the things he believed in," Howard said.

Jack Straw, Cook's successor as foreign secretary, said he was "devastated."

"Robin and I had been good friends for nearly 30 years and that friendship survived our policy disagreements over Iraq," Straw said. "He was the greatest parliamentarian of his generation and a very fine foreign secretary. I deeply mourn his loss."

Cook served as foreign minister in 1997-2001 before being demoted to leader of the House of Commons. His resignation speech, days before the Iraq war began in March 2003, received a rare standing ovation from lawmakers.

"Why is it now so urgent that we should take military action to disarm a military capacity that has been there for 20 years, and which we helped to create?" he said.

Renowned as an intelligent lawmaker and skilled debater, Cook remained a high-profile figure despite his withdrawal from government, and he became an increasingly vocal opponent of Blair's policies.

Some supporters believed Cook should have been leader of the Labour Party (search). But opponents saw him as arrogant and distant.

A lawmaker since 1974, Cook — a short, bearded redhead — declined to oppose Blair when he was elected Labour leader in 1994, declaring: "I am not good-looking enough."

Instead, Cook accepted the post of foreign secretary following the landslide election victory that made Blair prime minister in 1997.

But his promise of an "ethical dimension" to British foreign policy often came back to haunt him, particularly after he sanctioned the sale of 16 Hawk jet fighters to Indonesia in 1999, despite the country's widely criticized human rights record in East Timor (search).

Another diplomatic miscalculation came during a trip to India and Pakistan, when he suggested that Britain could mediate any negotiations over the disputed territory of Kashmir. The remark irritated both countries.

Cook was praised by many for his tough-minded handling of the 1999 Kosovo crisis, but that and other successes were partly overshadowed by the scandal of ending his 28-year marriage to his wife, Margaret, at an airport as they were about to leave on vacation.

Warned by Downing Street that a tabloid newspaper was about to disclose his long-standing affair with his secretary Gaynor Regan, Cook immediately told Margaret he was leaving her. Margaret Cook wrote a book accusing her former husband of being a drunk and a depressive.

She said his intelligence and ability were unmatched, but he had "absolutely no natural courtesy or sympathy."

Cook, who later married Regan, shifted to the right of the party under Blair's leadership but gravitated back to the left following his demotion, earning a reputation as a leading Cabinet "dove" opposed to invading Iraq without a U.N. mandate.

An ally of Treasury chief Gordon Brown, Cook had been tipped to return to Cabinet should Brown succeed Blair as Labour leader, as many predict.

On Saturday, Brown praised Cook's "incisive mind, forensic skills and formidable and wide-ranging debating prowess."

"A strong European, a committed internationalist, and a distinguished foreign secretary with friends in every country, he will be mourned greatly not only by his family, friends, colleagues and constituents, but in every continent of the world," Brown said.

Cook is survived by his wife and two sons from his first marriage.