Born in 1953, McCaskill was first raised in Houston, where her father William worked at the McCaskill Feed Mill. The family later settled in the northern Missouri city of Columbia, where McCaskill graduated from high school. There, her father worked as a state insurance commissioner and her mother, Betty, became Columbia's first female city council member.

After high school, McCaskill remained in Columbia to attend the University of Missouri's undergraduate and law schools, graduating in 1975 and 1978, respectively. She then moved to Kansas City to clerk for a judge on the Missouri Court of Appeals and later became an assistant prosecutor for the Jackson County Prosecutor's Office. During this time, she also joined the Catholic Church, despite her initial concerns it would complicate her political views on abortion and divorce.

In 1982, McCaskill was elected to the Missouri House of Representatives, where she served until 1988. In the state legislature, McCaskill chaired the House Civil and Criminal Justice Committee, along with the Budget and Judiciary committees. She also became the first woman to have a baby -- her first child Austin -- as a state lawmaker.

In 1992, Claire was elected as Jackson County prosecutor, becoming the first woman to head the largest prosecutor's office in the state. She was reelected county prosecutor in 1996, where she remained until she was sworn in as Missouri state auditor in 1999.

In April 2002, McCaskill got remarried to St. Louis businessman, Joseph Shepard. Together they have seven children -- Benjamin, 28, Carl, 23, Marilyn, 23, Michael, 21, Austin, 16, Maddie, 14, and Lily, 11 -- four from his previous marriage and three from her previous marriage.

During her first term as state auditor, McCaskill received an award from the Missouri Press Association for her series of audits on the performance of state agencies in complying with public record requests under the state's Sunshine Law.

McCaskill began her second term as state auditor in 2003, though the year before she had already announced her intentions to run for governor. She said she had her eye on the 2008 election, although she cautioned "you never know what'll happen in politics."

She did reassess her decision as 2003 wore on and as incumbent Democratic Governor Bob Holden continued to face opposition from the state legislature. Following a record number of votes to override Holden's veto, McCaskill announced she would take on Holden in the primary.

Indeed, in a particularly bitter Democratic primary, McCaskill defeated Holden 52 percent to 45 percent. Immediately after the divisive primary, however, the state Democrats sought to present a united front against "favorite son" Matt Blunt, the Republican gubernatorial contender and son of Republican Rep. Roy Blunt.

McCaskill has described the auditor's office as a great place to learn the ins and outs of state government.

"Somehow in the public sector, if you start in the mailroom and spend your life getting promoted, it's unseemly," she said in a 2002 interview with a local news service. "I started in the mailroom, literally, as an intern ... in 1974. The legislator I was working for at the time said, 'I want you to get your law degree and come back here and get elected and be the first woman governor.' I kind of took that guy seriously -- I thought that sounded like a pretty good idea."

On the campaign trail, McCaskill has pointed to her record as state auditor who has fought aggressively against government waste and fraud, pledging to do the same if elected governor. She also vows to not raise taxes by streamlining government services and eliminating unnecessary expenses. To distance herself from Holden, she says she will handle the state budget and education expenses differently.

McCaskill surprised many with her success in reaching swing voters and even those in rural areas, considered a Republican stronghold. She also surprised pundits by her fundraising prowess -- pulling in a total of $5.7 million as of early September, even surpassing Blunt's campaign coffers. She did acquire a $1.6 million debt after using her own funds to help pay for the competitive, tight primary race.

Her strong primary victory -- as well as her energy and drive -- have heightened Democrats' hopes to secure the governor's office for a second term, even with a new candidate.