"I would not say that the future is necessarily less predictable than the past. I think the past was not predictable when it started." — Donald Rumsfeld

Donald Rumsfeld addresses military personnel at the Abu Ghraib Prison near Baghdad in 2004. (Jim MacMillan/AP)

Donald Rumsfeld's exit from George W. Bush's cabinet ends another chapter in his long political life that began in the 1960s and spanned the rule of four presidents. His latest role as Secretary of Defence might well become a stint that will define him. It saw him take the spotlight when his country was attacked, launched its war on terror and felt the domestic backlash, initially for prison abuses in Iraq and finally for U.S. involvement in the country altogether.

Rumsfeld's tenure in Washington's power circles has included stints serving under the following presidents: Richard Nixon, Gerald Ford, Ronald Reagan and George W. Bush. When he took the post as Secretary of Defence in January 2001, it was the second time he served in that role. The last time was under Ford from 1975 to 1977.

Donald Rumsfeld's career in brief:

• Born in Evanston, Illinois, in 1932
• Princeton educated, served in Navy
• Elected in 1962 to House of Representatives at age 30
• Served as Secretary of Defence in 1975-1977 (Nixon) and 2001 to 2006 (Bush)
• Has won Medal of Freedom

Observers claimed Rumsfeld's naming to the Defence Secretary post in 2001 was a signal that then president-elect George W. Bush intended to radically change the country's military policy, because Rumsfeld would be in a good position to promote establishing a National Missile Defense shield. The controversial plan would allow the U.S. to destroy enemy long-range rockets from land, sea and space. Just prior to his appointment, Rumsfeld had released a report assessing U.S. security in space. Critics dubbed Rumsfeld "Darth Vader," calling his vision for an American military presence in space fanatical and reminiscent of Cold War paranoia.

On Sept. 11, 2001, Rumsfeld was in his Pentagon office discussing missile defence with a delegation from Capitol Hill when a hijacked aircraft struck the opposite side of the building. As the country lurched into a terror alert, Rumsfeld was among the hawkish advisers surrounding Bush in the West Wing to plan a response.

"Look, I'm old fashioned. I always believed that you don't cock [your arm] you throw it. You don't talk about it. You do it," Rumsfeld said, when asked if the administration would respond aggressively to the attacks.

He backed up his words with action. Less than a month after the Sept. 11 attacks, Rumsfeld was planning "Operation Enduring Freedom" in Afghanistan and giving daily, televised press conferences about the war's progress.

Key player in Iraq invasion

As the war in Afghanistan raged on, Rumsfeld began drawing up a new a plan to invade Iraq in November 2001, reasoning to ABC News that the United States would root out suspected "weapons of mass destruction" that Intelligence reports suggested were "in the area of Tikrit and Baghdad and east, west, south and north somewhat."

Bush launched the invasion of Iraq in March 2003, despite skepticism from critics that there were likely no WMDs there. Responding to concerns about looting in Iraq during the 2003 U.S. invasion, Rumsfeld suggested the unrest was "part of the price" to pay for what the United States and Britain were calling the liberation of Iraq and that "stuff happens." Rumsfeld argued conditions would improve once Iraq dictator Saddam Hussein was overthrown.

By May 2003, it was evident Iraq was still in great turmoil in the aftermath of the invasion. Critics said post-war planning to secure the country was mishandled. The Iraqi Army disbanded, leaving the U.S. military alone to handle security and reconstruction. Meanwhile, widespread civil unrest grew into an insurgency against coalition forces and the U.S.-backed Iraqi government.

In April 2004, a CBS report broke a shocking story about abuse of Iraqi detainees at Abu Ghraib prison. Calls began for Rumsfeld to resign amid the scandal. Then in November 2006, the influential military publication the Army Times wrote that Rumsfeld must go. In his editorial, neo-conservative Richard Perle, who chaired a committee of Pentagon policy advisers early in the Bush administration, admitted he would not have supported the Iraq invasion if he had known what the outcome would have been. A day after the Republicans lost control of the House of Representatives in the November 2006 mid-term elections, Rumsfeld resigned his position.

Political life started at 30

Born in Evanston, Illinois in 1932, Rumsfeld went to Princeton University. He has a background in the military, having served as a flight instructor in the mid-1950s in the U.S. Navy. He entry into politics came when he was elected to the U.S. House of Representatives from his home state when he was 30, in 1962. He got his first cabinet post in 1969 and stayed there until 1972, during which time he advised then-president Nixon on economic matters. In 1974, Rumsfeld became the White House chief of staff under Ford, and a year later Rumsfeld was named Secretary of Defence. During his first stint in the post, he pushed for Washington to boost the military in light of the threat from communist Russia and he oversaw reforms, notably changing the military to a volunteer organization. He was given the Presidential Medal of Freedom in 1977.

Under president Reagan, Rumsfeld was the special envoy to the Middle East from 1983 to 1984. He met with Saddam while Washington was weighing in on the Iran-Iraq war. This relationship, and in particular a picture of him shaking hands with Saddam in 1983, would come back to haunt Rumsfeld.

Rumsfeld has spent a few years in the private sector, away from the political sphere, as CEO of G.D. Searle & Company, a pharmaceutical firm, and also the head of General Instrument Corp. in the early 1990s.

Rumsfeld quotables:

"Death has a tendency to encourage a depressing view of war."

"Reports that say that something hasn't happened are always interesting to me, because as we know, there are known knowns — there are things we know we know. We also know there are known unknowns — that is to say we know there are some things we do not know. But there are also unknown unknowns — the ones we don't know we don't know."

"It is unknowable how long that conflict will last. It could last six days, six weeks. I doubt six months." Rumsfeld made this statement to U.S. troops in Aviano, Italy, in 2003.

"We acted in Iraq because we saw the evidence in a dramatic new light — through the prism of our experience on 9/11."

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