NEW YORK  – As a single mother with a British accent who loves numbers, Marianne Lake bears little resemblance to Jamie Dimon, the longtime chief executive of JPMorgan Chase & Co (JPM.N), known for his bravado, quips and occasional profanity-laced outbursts.

Yet Lake has emerged as a front-runner to replace Dimon when he eventually retires, Reuters interviews with more than a dozen current and former executives show.

Over her nearly six years as JPMorgan’s chief financial officer Lake, 49, has taken on more and more responsibilities effectively becoming Dimon’s understudy. She helps develop strategies for each of the bank’s business units and oversees matters ranging from its annual stress test to employee cafeterias.

Largely unknown outside JPMorgan when named CFO in 2012, Lake has worked in both the wholesale and retail businesses during 19 years there. “She has been all over,” Dimon, 62, said in an interview, describing Lake as an “extraordinarily talented executive.”

“She has all of the qualities of a great leader,” he said. Those include being demanding, drawing information out of people and recognizing talent within the 15,000 people she oversees. Dimon said she also challenges him when she believes he is wrong.

Lake, who also spoke to Reuters, said she wanted to broaden her skillset in her next job and has made her ambitions clear to the board chaired by Dimon. She declined to predict whether she will be the next CEO.

“I want to be at this company 10 years from now and I will be quite open-minded about what the next step could look like,” she said. “I have told the board that I want to be here for the long-term.”

Dimon has been CEO for nearly 13 years, the longest tenure among major U.S. banks. He is a larger-than-life figure who steered JPMorgan through the financial crisis and regularly stands up to regulators and politicians. The question of who could succeed him has captivated Wall Street for years. (Graphic: tmsnrt.rs/2NbTiZo)

Lake’s standing has risen as other CEO candidates have left JPMorgan after growing impatient or getting on Dimon’s wrong side, executives said. “I would put my money on her above anybody else,” said one longtime JPMorgan executive who spoke on the condition of anonymity.

“She knows the bank extremely well, with her role spanning all of our businesses and functions,” said Gordon Smith, co-president of the company and chief executive of JPMorgan’s consumer bank.

Dimon, who has said he will step down in about five years, would not discuss Lake’s chances. It is the board’s choice, and there are other people who could also run the company, he said. And, Dimon cautioned, “Things change…Everybody changes.”

JPMorgan has said it has a succession plan and that it strives to give executives experience in its different businesses, but it does not publicly disclose the details.

Two people analysts often mention as possible successors if Dimon were to suddenly leave are Smith, 60, and the other co-president Daniel Pinto, 55, who runs the investment bank. Mary Erdoes, 51, chief of asset and wealth management, and Doug Petno, 53, chief of the commercial bank, have also been cited over the years.

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When former CFO Douglas Braunstein stepped down in 2012 in the wake of the “London whale” scandal in which a JPMorgan trader lost more than $6 billion, Lake was one of several executives interviewing for the CFO job. In the interview, Lake credited a colleague for a piece of advice she says helped her win the promotion: Tell Dimon how much you want the job and tell him how hard you will work for him.

“If you don’t tell people you really want a job, then you have no shot,” said Lake.

Born in Maryland and raised by working-class parents in southern England, Lake joined JPMorgan’s London office as chief financial officer for credit trading at age 30, after working on the JPMorgan account for PricewaterhouseCoopers accounting firm. She moved to the United States in 2004 as JPMorgan was merging with Bank One, which Dimon ran before becoming CEO of the combined organization.

She worked on an expensive, multi-year drive to combine JPMorgan’s data and accounting systems and the implementation of Sarbanes-Oxley accounting controls. She was controller of the investment bank during the 2007-2009 financial crisis, and ran finances for the retail bank as the mortgage business went through drastic changes afterward.

Dimon named her to the current post in November 2012 and colleagues were stunned by her intensity in preparing for her first quarterly results presentation in January.

“She always wants to understand the why behind the things she would say,” recalled Sarah Youngwood, then head of investor relations. “It is still happening to this day.”

Lake talks too fast for some people to keep up. “That is because she thinks so fast, but she has slowed it down,” said Youngwood, who now has Lake’s old job of CFO for the consumer bank.

Lake said she sometimes counts to herself to reduce the pace.

Bank analysts say they welcome all of the information Lake packs into her presentations and they like that she is quick to thoroughly address questions on investor minds.

For example, after Goldman Sachs analyst Richard Ramsden published a report in January 2015 asking whether JPMorgan should break itself up because of new regulations, Lake made a case that the bank would thrive because of its size.

“She is probably one of the most gifted CFOs around,” Ramsden said. “She is really at the top of every dynamic at JPMorgan.”

Lake’s speed, demands for information, and visual memory of numbers can intimidate new hires, people who work with her said. Dimon said he and Lake sometimes challenge one another to remember numbers down to one decimal point. “We have a lot of fun with each other,” he said.

Lake had her three children through a surrogate starting at the age 42 after she decided that, even without a partner, she wanted to be a parent. She said she realized after she became CFO that her story could inspire other career-driven women at the bank and she tells it frequently. One junior colleague described Lake’s parenting decision as “fearless.”

“It’s too easy to say it’s not convenient right now” to have a child, said Lake. “On big life-changing decisions like that, you just have to go for it.”

In a nod to her expanding role, JPMorgan put Lake at center stage at its four-hour investor conference this year. Typically, all the business heads would give their own presentations, but this time, Lake spoke for an hour and a half, explaining strategies for each of JPMorgan’s four segments and giving an overview of how the bank is using technology to cut costs and generate more revenue.

Lake says she is ready to take on a different role at JPMorgan and that the next CEO’s main challenge will be making sure JPMorgan remains the country’s most profitable big bank.

“When you are a successful company,” she said, “you have to fight really hard to make sure you avoid complacency, arrogance, bureaucracy.”