Chuck Hagel, the former Republican senator nominated as the next US defense secretary, is a decorated Vietnam veteran who will bring a skeptical eye to both military intervention and the Pentagon budget.

Hagel, 66, is known for a fiercely independent streak and a tendency to speak bluntly, falling out with his fellow Republicans over the Iraq war.

If confirmed by the Senate as Pentagon chief, Hagel will have to manage major cuts to military spending while wrapping up the US war effort in Afghanistan and preparing for worst-case scenarios in Iran or Syria.

Hagel will likely face a rough reception in his confirmation hearings from his fellow Republicans, some of whom accuse him of harboring hostility towards Israel while being naive when it comes to dealing with Iran.

But President Barack Obama called Hagel, who would be the first enlisted veteran as defense secretary, "an American patriot." Obama said Hagel earned his respect when they travelled together as senators.

"I came to admire his courage, his judgment, his willingness to speak his mind, even if it wasn't popular, even if it defied conventional wisdom," Obama said.

Although Hagel had a mostly conservative record as a senator, his Republican colleagues have never forgiven him for his outspoken criticism of ex-president George W. Bush's handling of the Iraq war.

He called the administration's effort at the time "beyond pitiful" and when Bush planned a surge of additional troops in 2006, Hagel said it was "the most dangerous foreign policy blunder in this country since Vietnam, if it's carried out."

Born in North Platte, Nebraska, Hagel grew up in a poor family, working at odd jobs starting at age nine to help put food on the table and stepping in to protect his mother from a sometimes abusive, alcoholic father.

In Vietnam, Hagel served as an infantry squad leader and saw combat first-hand in the jungles of the Mekong Delta, earning two Purple Hearts after suffering shrapnel wounds to his chest and burns to his face. He still has some shrapnel fragments lodged in his chest.

The searing experience in Vietnam has stayed with him, leading him to view military action as a last resort, after all diplomatic tools have been exhausted.

"Chuck knows that war is not an abstraction. He knows that sending young Americans to fight and bleed in the dirt and mud, that's something we only do when it's absolutely necessary," Obama said.

He and his brother, Tom, served in the same unit and each saved the other's life in separate, harrowing incidents.

Tom stanched the bleeding from a chest wound Hagel had suffered. A few weeks later, Hagel pulled his unconscious brother to safety from an armored personnel carrier after it struck a land mine.

Upon returning from Vietnam, Hagel held an array of jobs, including as a radio reporter, before landing a position on the staff of a Nebraskan lawmaker in Congress, where he excelled.

After a stint at the Veterans Administration, and a clash with its chief, Hagel eventually got in on the ground floor of America's cell phone industry, becoming a multi-millionaire.

Moving back to Nebraska, Hagel was elected to the Senate in 1996 and again in 2002. He considered running for president in the 2008 race but opted against a bid, partly because of his strained relations with the party's leadership and his outspoken opposition to the Iraq war.

Although he mostly shares Obama's views on foreign policy, Hagel has not hesitated to express his differences with the US president, such as when the White House incumbent unveiled a troop surge in Afghanistan in 2009.

"I'm not sure we know what the hell we are doing in Afghanistan," Hagel said the following year. "It's not sustainable at all. We're marking time as we slaughter more young people."

In his typical straight-shooting fashion, Hagel has called the Defense Department "bloated" and said that "the Pentagon needs to be pared down."

Even some Democrats have reservations about Hagel due to comments he made in the 1990s criticizing the choice of an openly gay man as an ambassador. He has since apologized and voiced support for gay rights.