By Randall Palmer and David Ljunggren
OTTAWA (Reuters) - The left-wing leader in striking distance of toppling Canada's Conservative prime minister was once known as "Angry Tom," but Thomas Mulcair has been turning on the charm to convince voters he is ready to run the country.
The 60-year-old Mulcair, who inherited Canada's opposition New Democratic Party after his charismatic predecessor died in 2011, holds a slim lead in a tight, three-way race ahead of the Oct. 19 general election, according to the latest polls.
Described as "smart, tough and nasty" by Canadian magazine Maclean's in 2012, the man who decided on a career in politics when he was 14 has spent the last three years taming what he once called "a good Irish temper."
"The biggest challenge with Tom was always Tom himself, because he had a tendency of going over the top," said a former colleague in the province of Quebec, where Mulcair started his political career.
"But since he's been in federal politics, I've been impressed by two things: how much he's disciplined himself and how much he's disciplined his caucus."
In 2005, Mulcair was ordered to pay another Quebec politician C$95,000 ($77,017) for defamation after he accused the politician of influence peddling.
Five years later, during a televised exchange, Mulcair snapped "You're a crap journalist" to a reporter for Maclean's, which had called Quebec Canada's most corrupt province.
In 2011, after U.S. President Barack Obama announced the killing of Osama bin Laden, Mulcair said he did not think the United States had pictures of the corpse. He later blamed election "fatigue" for his remark.
In the last three years, such outbursts have all but disappeared, even as Mulcair hammered Conservative Prime Minister Stephen Harper again and again in Parliament on issues ranging from security to the economy and the environment.
Mulcair's moderated behavior has impressed some officials from the other end of the political spectrum: former Conservative Prime Minister Brian Mulroney has called Mulcair the best opposition leader in more than 50 years.
Others say the NDP leader's temperament remains a wild card.
"I don't think the public yet knows Mulcair, let alone have made peace with 'Angry Tom,'" said former Harper spokesman Andrew MacDougall.
"Let's remember that Mulcair hasn't been the figurehead of a national political campaign. While he's a veteran politician, he'll get more scrutiny than ever before, and it remains to be seen how he'll handle it."
Mulcair's aides declined to make him available for an interview. His principal secretary, Karl Belanger, dismissed such criticism as groundless attacks by opponents and pundits.
"Canadians see Tom Mulcair for what he is - a principled leader, standing up for middle class families and fighting with passion for social justice, a stronger economy and a cleaner environment," he said.
The once-socialist NDP was formed in 1961 and until 2011 had never even come second in a federal election. The party's rise this year in key battlegrounds, such as Ontario and Alberta, has elevated Mulcair from a relative unknown to a possible replacement for Harper, who has been in power since early 2006.
Mulcair opposes nearly all of Harper's agenda, including Canada's military role against Islamic State and anti-terror legislation that expands the government's spying powers.
The NDP leader has proposed raising corporate taxes to help fund a national daycare program, increase the minimum wage for federally regulated companies, and improve transit, healthcare and housing. (FACTBOX on NDP policies)
A Forum poll last week put support for the NDP at 36 percent, ahead of the Conservative Party and Justin Trudeau's Liberal Party, which were tied at 28 percent.
"We've always assumed Trudeau was going to be the main threat but perhaps it will be Mulcair," one senior Conservative said after the NDP's shock victory in May in Alberta, a long-conservative province.
Mulcair is the second eldest of 10 children born to a French-Catholic mother and an Irish-Catholic father in Quebec. He studied law at university and became a citizen of France after his marriage in 1976 to a French-born psychologist, Catherine Pinhas. He has voted in France's elections, but has said he would give up his French citizenship if he becomes prime minister.
Mulcair worked for a time as a lawyer before entering politics in 1994 as a legislator for the centrist Liberals in Quebec. He became a cabinet minister for the Quebec Liberals in 2003, and resigned three years later after clashing with his own government over a real estate development plan. He joined the federal NDP in 2007.
Voters have rarely seen Mulcair except on attack, and the bearded, burly leader has a stare that can be intense. He earned the nickname "prosecutor-in-chief" in 2013, when he used his lawyer skills to grill Harper over his office's role in an expenses scandal.
Friends say Mulcair, who has two sons and two grandchildren, is loyal and funny, driven by a social responsibility taught at home.
"When you're having dinner with Tom the laughter is constant," said Julius Grey, a Montreal-based lawyer. "He's not a somber policy wonk."
($1 = C$1.2335)
(Additional reporting by Allison Lampert in Montreal; Editing by Andrea Hopkins and Tiffany Wu)