What is Hagel's background?
He comes from humble stock. Born in Nebraska, Hagel grew up poor and constantly on the move. His father was a World War II veteran who had bad health and a drinking problem, and died when Hagel was 16. The eldest of four boys, Hagel worked to help support the family, and took an early interest in politics. In 1960, he broke with his fellow Catholic schoolboys to support Richard Nixon over John F. Kennedy. Hagel was a promising high school athlete, but a neck injury forced him to give up a college football scholarship. He drifted until his number came up in the draft in January 1967.

Where did he serve?
Hagel initially received orders to go to Germany, but he asked for a transfer to Vietnam so he could fight in the war. Against protocol, he was placed in the same infantry squad as his younger brother Tom. Just four months into his tour, Hagel was caught in a mine blast, taking shrapnel wounds to his chest that his brother bandaged up. A month later, in April 1968, Hagel returned the favor after their troop carrier hit another mine. Hagel pulled Tom from the burning vehicle under heavy fire, sustaining serious burns to his face. (Hagel's wounds in the two incidents won him two Purple Hearts.) In 2007, he recalled what went through his head when rescuing his brother: "I told myself, 'If I ever get out of this and I'm ever in a position to influence policy, I will do everything I can to avoid needless, senseless war.'"

How did he get into politics?
John Y. McCollister, a Nebraska congressman, brought the young veteran to Washington in the early 1970s; within 18 months, he was McCollister's chief of staff. Hagel's ascent in the Republican Party was similarly rapid, and soon after Ronald Reagan was elected in 1980, he was named deputy director of the Veterans Administration. But within six months, he quit in protest against cuts in benefits for his fellow Vietnam veterans. It was his first act of rebellion against the party, but far from his last. "He thinks with the clarity of an actuary," said Michael McCarthy, one of Hagel's longtime financial backers, "but decides with the heart of an Irishman."

What was his next move? 
He sold his car and joined two friends in investing in an industry no one knew about in 1982 — a cellphone company. It made him millions when it later went public. In 1992 he moved his family from Virginia back to his native Nebraska, where he was elected senator in 1996 in an upset victory after a high-profile endorsement from fellow Vietnam vet Sen. John McCain. But Hagel remained a party maverick. After the GOP's poor showing in the 1998 midterm elections, he excoriated the leadership for running "issueless campaigns" and "demonizing" ads. In the 2000 primaries, he backed his friend McCain, saying that George W. Bush had "sold his soul to the right wing." Two years later, he became an ever bigger burr in Bush's saddle.

What issue divided them?
The war in Iraq, which Hagel opposed from the get-go, earning himself a place on the "axis of appeasement'' compiled by the neoconservative magazine The Weekly Standard. In 2002, Hagel delivered a thunderous speech on the Senate floor warning that "imposing democracy through force is a roll of the dice." The U.S., he said, did not truly understand the factional divisions among Iraq's Shiites, Sunnis, and Kurds. He then voted to authorize military action in Iraq — a vote he attributed to his loyalty to the office of the presidency. As the war spun out of control, Hagel became an ever-fiercer critic of the Bush administration. He voted against extending the Patriot Act in 2005, and led opposition in the Senate to the Iraq surge of 2007, calling it the "most dangerous foreign-policy blunder in this country since Vietnam."

Is that why many Republicans now oppose him?
Hagel's apostasy on Iraq is just one of the ways in which he has infuriated his party's hawks. He has opposed military action to stop Iran's nuclear program, and described the Defense Department as "bloated." He angered pro-Israeli Republicans by complaining about the power of Washington's "Jewish lobby," and alienated social conservatives by comparing them to "Know-Nothings." But arguably his greatest sin against the GOP was befriending Obama. The two bonded in the Senate over their contrarian views on Iraq. In 2008, Hagel declined to endorse John McCain, which brought a chill to the long friendship between the two Vietnam vets. Hagel did not endorse Obama either, but enraged McCain by traveling to Iraq with the Democratic presidential candidate in July 2008. Hagel retired from the Senate in 2009, but he will soon return there as Obama's nominee for defense secretary to face confirmation hearings headed by his spurned former ally. "The friendship, I hope, is still there," McCain said in January, "but I have very serious questions about whether he will serve in a way that I think serves America's best national interests."

The smoking gun on Vietnam
Although the Vietnam War left Hagel scarred, for decades he saw it as a righteous cause gone wrong, not an unjustified incursion. That changed in 1997, when the government released tapes from 1964 of Lyndon B. Johnson confessing that the U.S. couldn't win in Vietnam. Johnson had made a "cold political calculation" to stay in Vietnam to secure his legacy, Hagel came to believe, and he vowed to "never, ever remain silent when that kind of thinking put more American lives at risk in any conflict." His anti-war views hardened yet further in 2005, when a cousin unearthed long-lost letters his father had written to his family during his service in the Pacific. "If I thought I would ever have a son who would have to go through this," he had written, "I would never get married."