This story has been updated.

Scott Walker, the polarizing Republican governor of Wisconsin who catapulted to national prominence after severely weakening public-sector unions in his state and facing a contentious recall election, announced Monday morning that he is running for president.

"I am running for president to fight and win for the American people," Walker said in a video. "Without sacrificing our principals, we won three elections in four years in a blue state. We did it by leading. Now, we need to do the same thing for America. It's not too late. We can make our country great again."

This a decision that Walker, 47, says he has been thinking and praying about for months with his wife, Tonette Walker, and their two college-aged sons. He has also been traveling nearly nonstop this year, cramming on foreign policy, raising money and building support.

"Heck, even being one of 50 people in America to be a governor is unbelievable for a kid who grew up in a small town with a dad who was a pastor and a mom who was a part-time secretary," Walker said in a radio interview last week. "Maybe the last four years was a little bit of God’s providence. We wanted to make sure that … we weren’t living in a bubble."

Walker will also gather Monday evening with a crowd of supporters at the Waukesha County Expo Center, an events center in Milwaukee’s deeply conservative exurbs where the governor celebrated winning his recall election in 2012. That election as the result of Walker weakening many of the state’s most powerful unions, generating national news and exposing Walker to wealthy donors who could now help him with a run for the White House.

The Midwesterner presents himself as a steadfast conservative who will not back down from a fight from liberals and who knows how to beat Democrats. Last week, Walker’s campaign released a video, "Recall the Recall," that recounts the governor’s fight with the unions with the tone and pacing of an action movie.

"He took big, bold action," the narrator says as black-and-white video footage plays, later turning to color. “The left erupted. They stormed the capital. But Scott Walker stood his ground, unintimidated. They even threatened his family, but he stood firm. And he won. The battle left the big-government, special interests crippled. But the real winners? Children, taxpayers, seniors.”

Walker continued that messaging in his announcement video and used it to contrast himself to the other Republicans who are running for president.

"In the Republican field, there are some who are good fighters, but they haven't won those battles. There are others who have won elections but haven't consistently taken on the big fights," Walker said. "We showed you can do both."

Later this week, Walker will visit five early primary voting states in six days – Nevada, South Carolina, Georgia, New Hampshire and then Iowa, where he will spend three days crisscrossing the state in a Winnebago. The whirlwind trip includes visits to at least four stores that sell Harley-Davidson motorcycles, a Wisconsin-based company that Walker likes to plug.

Walker’s aides say they are determined to win Iowa. Walker was the first major potential candidate to lease office space there, and he has hired strategists who advised Sen. Joni Ernst (R-Iowa) during her high-profile win last year. Walker has visited Iowa at least half a dozen times so far this year, talking about his Midwestern roots and often out-spending other candidates. At the Iowa GOP Lincoln Dinner in May, Walker threw a glitzy post-party, complete with a DJ, huge chunks of Wisconsin cheese, a photo booth with a Harley and posters featuring quotes from Walker. The campaign also aims to finish well, like in the top three, in New Hampshire and South Carolina, where Walker has spent much less time.

Soon after Walker's video went public, the attacks began. AFL-CIO President Richard Trumka, who fought Walker's dramatic labor reforms, put out a six-word statement: "Scott Walker is a national disgrace."

The Democratic Party tweeted out a quick video clip of Walker saying the only way he would be a viable presidential candidate is if things were going well in Wisconsin:

Pro-immigration and abortion rights activists also criticized Walker as too conservative. “Scott Walker has proven himself to be a terrible governor of Wisconsin, and a Walker presidency would be even worse for Latinos and for our nation as a whole," labor and civil rights activist Dolores Huerta said in a statement.

Erika West, the political director at NARAL Pro-Choice America, said Walker "threw Wisconsin women under the bus to score points with a few right-wing voters in Iowa" by supporting a ban on abortions after 20 weeks.

Although Walker has spent nearly his entire adult life in politics, he casts himself as an average guy who is in touch with working and middle-class families. He routinely slams D.C. as being “68 square miles surrounded by reality.” And in a race that already involves two wealthy candidates from well-known political families – Hillary Rodham Clinton and Jeb Bush – Walker often talks about growing up without much money in a small town and says his family still lives modestly, packing brown-bag lunches and using coupons at Kohl’s department store.

“Unlike some out there, I didn’t inherit fame or fortune from my family,” Walker said in a speech in Nashville earlier this year, a line that he often repeats. “I got a bunch of things that were a whole lot better than that. I got from my parents and my grandparents the belief that if you work hard and you play by the rules and you’re in America you can do and be anything that you want. That’s a powerful belief.”

[Scott Walker's wife, toughened by life, is ready for the fires of a presidential campaign]

Scott Kevin Walker was born in Nov. 2, 1967, in Colorado Springs. At a young age, his family moved to Plainfield, a small town in northeast Iowa where his father, Llew Walker, was a Baptist pastor and his mother, Pat Walker, did bookkeeping work. At one point, Walker and his younger brother, David, realized that the local city hall didn’t have a state flag, so they washed out a mayonnaise jar and walked around town collecting donations for one.

In 1977, the family moved to Delavan, Wis., where Walker attended high school, participated in Boys State and earned the rank of Eagle Scout. Old photos show Walker sported a mullet hairstyle. He often talks about saving up money to pay for college by washing dishes at a Countryside restaurant and then flipping burgers at a McDonald's – at about the same time that Wisconsin Rep. Paul Ryan (R-Wis.) was working at a McDonald's in Janesville, about 15 miles down the road.

"The only difference is his manager told him he had to work the back flipping hamburgers because he didn't have the interpersonal skills to work the front cash register," Walker likes to tell audiences, always prompting laughter.

Tonette Walker looks toward her husband, Scott Walker, during the Chad Airhart Blue Jean Bash fundraiser in West Des Moines, Iowa, on May 16. (Daniel Acker/Bloomberg)

The two Wisconsin Republicans are close, although Ryan is staying neutral in the primary. Mitt Romney named Ryan as his running mate during the last presidential election, and a tear slid down Walker's cheek when Ryan spoke at the Republican National Convention.

"Paul is one of the smartest and most courageous people I know in politics. He is also one of the most decent," Walker wrote in his 2013 book, "Unintimidated." "I was overwhelmed with pride."

In 1986, Walker enrolled at Marquette University, a Jesuit Catholic private school in Milwaukee. Walker was known for wearing suits to class and being obsessed with Ronald Reagan. Even then, Walker was involved in politics and talked about running for president. One former classmate recalls calling Walker "Niedermeyer" after the power-hungry character on the movie "Animal House." In 1990, Walker mysteriously left college without graduating. He was at least 34 credits short, according to the Milwaukee Journal Sentinel.

[Read more: As Scott Walker mulls White House bid, questions linger over college exit]

Walker took a job at the local American Red Cross and soon was running for the state house, a race that he lost. He has said that he had eventually wanted to finish up his degree, but got caught up with work and family.

In 1992, Walker met his future wife, Tonette Tarantino, a young widow and Catholic Democrat who grew up on the east side of Milwaukee and is a dozen years older than him. Months after meeting, Walker proposed and the two married in February 1993 on Reagan's birthday. Four months later, Walker was elected to the state assembly, where he championed tough-on-crime reforms and several anti-abortion bills. He was re-elected four times. The couple has two sons, Matt and Alex, who are taking time off  from college to help with their dad's campaign.

In 2002, the Democratic Milwaukee County Executive resigned amid scandal and Walker ran in a special election to replace him. Soon after winning, Walker quickly began plotting a run for governor. His time as county executive become the subject of a secrecy-shrouded investigation that examined political work Walker's staff members did on county time, using a secret wireless router to avoid detection. That led to the conviction of six former aides and associates, including Walker's deputy chief of staff who is currently serving a jail sentence through house arrest. Later, prosecutors launched a second investigation probing accusations of improper coordination between Walker's recall election campaign and outside groups like the Wisconsin Club for Growth.

Walker has called these investigations a politically driven "witch hunt." He has never been charged in connection with them.

E-mails and court documents released as part of those investigations provided a rare look at how the politician operates. Walker -- who goes by "SKW" in emails -- is often humorless and to-the-point, a constant strategist who is obsessed with media coverage. A long-time associate says Walker has a rare gift of carefully tracking what he's hearing on the ground and then subtly shifting his messaging to better connect, although rivals have painted this as flip-flopping. While most presidential contenders decline to publicly discuss the details of their political strategy, Walker's voice picks up with excitement as he talks about the strong push he wants to make in neighboring Iowa and how he likely won't spend much in Florida, allowing Floridians Bush and Sen. Marco Rubio to blow through cash fighting each other. Wisconsin Senate President Mary Lazich, a Republican who is also from the Milwaukee suburbs, carpooled with Walker for years and doesn't remember ever discussing anything other than political strategy -- how to rally votes for legislation and what can be learned from previous races.

"He's a political animal," Lazich said in an interview. "I think he was born that way."

In 2006, Walker tried to run for governor but dropped out. He tried again in 2010 and was elected as part of a wave of Republican wins that year. Weeks after taking office in January 2011, Walker launched the attack on public-sector unions that would come to define him on the national stage. Walker had been frustrated with collective bargaining since his days as county executive, when he says that he was forced to lay off young workers because of seniority rules. He figured that the state could save millions of dollars by no longer bargaining with state employees on pay, lay-offs and benefits. These were entitlements the state could not afford, he said.

"We can no longer live in a society where the public employees are the haves and the taxpayers who foot the bill are the have-nots," Walker said in a speech in December 2010. "Public employees can't be the untouchables."

[Scott Walker's anti-union law has labor reeling in Wisconsin]

The backlash was swift and angry, with as many as 100,000 protesters descending on Madison. Republican lawmakers who dominate both chambers rushed to push the legislation through the statehouse, often using complicated maneuvers. At one point, Democrats fled the state to avoid a vote. Eventually, the changes -- referred to as "Act 10" -- passed. Union membership in the state plummeted, providing less dues and less resources to support Democratic lawmakers.

A protester holds a heart cutout in the Capitol as protesters staged a Valentine's Day demonstration against Gov. Scott Walker's anti-union legislation.

While visiting early-voting states, Walker always talks about these protests, which he says were the precursor to the Occupy Wall Street movement. Walker says that he and his family, along with other Republicans, faced harassment and death threats. Walker describes the scene as a war zone in his book, and he had to sneak out of the statehouse through tunnels and use decoy buses to fool protestors who might hurt him: "It was like a scene out of 'Call of Duty.'"

Activists then pushed for recall elections for Walker and other Republicans. These races attracted millions of dollars in donations from wealthy Republicans across the country who might typically not get involved in Wisconsin races but sympathized with Walker. The governor won the recall election and then was re-elected last year -- meaning that he has won three elections in four years in a state that for decades has voted for a Democrat for president.

Soon after winning in November, Walker has said that he and his family began discussing a possible run for president. In January, Walker started a political organization, Our American Revival, which has been funding his months of travel around the country. Walker's expected campaign manager is Rick Wiley, a longtime political operative and former RNC political director who has deep ties to Wisconsin. Wiley has a forceful presence -- a hulking, fitness-crazed Cubs fan with a shaved head and tiny chin-beard who is a prolific tweeter and frequent user of the word "bro." Unlike other campaign managers, Wiley frequently joins Walker on the road.

In April, two of Walker's former aides started a pro-Walker super PAC that can collect unlimited donations. It is called the Unintimidated PAC, borrowing the name from Walker's 2013 book. The PAC is run by Keith Gilkes, the strategist who played top roles in Walker's three gubernatorial races. His deputy is Stephan Thompson, who managed Walker’s 2014 campaign and was deputy manager of his 2010 bid.

Scott Walker, governor of Wisconsin, arrives to speak during the inaugural Roast and Ride in Boone, Iowa, on June 6. (Daniel Acker/Bloomberg)

Those two groups, along with another called "Friends of Scott Walker," have raised at least $20 million and hope to have at least $40 million by next year, according to aides. That's far less than Bush and Clinton have collected, but supporters of the governor remain confident that it will be enough to get his message out. Plus, Walker has said in interviews that Bush will likely burn through at least half of his money trying to win the Florida primary over Rubio.

[Ahead of 2016 launch, Scott Walker feuds with both parties at home]

One of Walker's first challenges is upping his name recognition, and he has been doing dozens of interviews with small market television stations and newspapers in key early-voting states. He also has struggled to speak about foreign policy with gravitas, prompting cram sessions with advisors and four foreign trips in five months. And while Walker has fought and defeated Democrats, this presidential primary will require him to spar with fellow Republicans -- and his usual tactic of writing off attacks as partisan or driven by a liberal media may no longer work. The past few months have been further complicated by problems at home, including a tight budget and Republican disagreement over how to pay for major transportation projects and a new professional basketball stadium.

Even though he's one of the last major candidates to get into the race, Walker has been passively attacking his rivals for months. Walker argues that while Republicans are "blessed" to have such a robust field, the candidates fall into two camps: U.S. senators who have challenged the Obama administration but have "yet to win any of those serious battles," and governors and former governors who are good at winning elections but have yet to  "consistently take on those big fights."

Walker pitches himself as the perfect blend of both. He also says enduring three polarizing elections in four years has fully vetted him and taught him how to stay on message.

"We would offer the unique perspective of someone who has done both, who has fought the good fight and who has won those fights time and time and time and time again," Walker said in a speech in Philadelphia last month. "I think in America… now more than ever wants someone in the White House who is not only going to fight but win for everyday taxpayers every single day they stay in office. That’s what I think the future holds if we elect the right person to be our next president."