Vietnam War veteran and four-term Arizona Sen. John McCain enters the 2008 presidential race as the presumptive nominee for the Republican Party with more than 40 years of political experience -- replete with both heroic accomplishments and bitter losses -- behind him.

Born to a military family at Coco Solo Naval Air Station in the Panama Canal on Aug. 29, 1936 , McCain's family moved to the northern Virginia suburbs of Washington, D.C., in 1951. Four years after graduating from a preparatory boarding school in Alexandria, Va., McCain followed in his father, naval officer John Sidney McCain Jr.'s, footsteps and entered the U.S. Naval Academy in 1958. He married his first wife, Carol Shepp, in 1965 and adopted her two young children.

During his military service as a Navy pilot in the Vietnam War, McCain narrowly survived a deadly firefight on July 29, 1967. Three months later, his plane was shot down over North Vietnam. Then a lieutenant commander, McCain was captured by Vietnamese operatives and held captive in a prisoner-of-war detention facility known as the "Hanoi Hilton" for more than five years. 

On March 14, 1973, McCain was released and returned to the United States. He began work as the Navy's liaison to the U.S. Senate in 1973, marking his entrance into the political arena. After separating from his first wife, Carol, in 1979, McCain married Cindy Lou Hensley in 1980. He retired from the military in 1981 as a captain.

While living in Phoenix in 1982, McCain ran his first successful campaign for Congress to become a U.S. House member. Four years later, McCain won the U.S. Senate seat of retiring Arizona Republican Barry Goldwater.

During his tenure in the Senate, McCain has taken a prominent position on many committees, including the Armed Services Committee, Commerce Committee and the Indian Affairs Committee.

In the mid-1980s, legal questions stirred over some of McCain's fundraising activities from 1982 until 1987, when he received $112,000 in political contributions from Lincoln Savings and Loan Association chief Charles Keating Jr. When the government investigated Keating's investment schemes, McCain was called upon, along with four other senators, to testify to the legitimacy of the business -- leading the group to be dubbed the "Keating Five." The Senate Ethics Committee ultimately concluded that McCain's involvement in the savings and loan controversy was minimal.

The Keating Five scandal prompted McCain to become a voice for stronger accountability and transparency in campaign finance law. In 1995, he worked with Sen. Russ Feingold, a Democrat from Wisconsin, to push forward campaign finance reform legislation. The Bipartisan Campaign Reform Act regulated certain types of campaign ads and imposed federal limits on political party committee fundraising.

In 1999, McCain published the memoir "Faith of My Fathers," and decided in 2000 to make his first run at president. He ran a competitive, yet unsuccessful campaign against then-Texas Gov. George W. Bush. In his race for the GOP nomination, McCain built his public image as a straight-talking maverick.

McCain remerged as a presidential candidate for the 2008 race -- although his bid suffered some rocky moments early in the campaign. The defeat of McCain-backed immigration reform legislation in 2007 had damaged his popularity among fellow Republicans on Capitol Hill. Later last year, the McCain camp cut staff due to a slowdown in fundraising amid rumors of internal staff disagreements. But key wins in New Hampshire's early primary and the multi-state primary contests on Feb. 5, 2008, breathed new life into his campaign. Subsequent victories in Texas and Ohio on March 4 helped him gain the delegates needed to claim the party's nomination.

McCain, 72, has suffered from three bouts of melanoma, for which he has had surgery, but recent health reports have indicated his cancer is in remission. He and Cindy live in Arizona. He has seven children and four grandchildren.

-- By Alexis Matsui, Online NewsHour