The Vanguard Group's chief investment officer, Mortimer "Tim" Buckley, has been named by the Malvern investment company's board to replace Bill McNabb as chief executive officer, by the end of the year. Bond chief Greg Davis, 46, will move up to Buckley's old job as CIO.

Customers' assets at Vanguard have quadrupled to around $4.4 trillion since McNabb succeeded John Brennan as CEO in 2008, while most other mutual fund companies lost customers. Brennan was 53 when he stepped down as CEO.

"I have been thinking about this transition for a year," McNabb told Bloomberg News. "Almost 10 years in this job is a long time, and Tim is so well-prepared to take over." McNabb will remain chairman of Vanguard.

In statements posted on Vanguard's website, Buckley tried to lower any expectations that stock prices will keep cooperating. "One of the early lessons in my career is that the financial markets will humble you," he said. "We've enjoyed a long stretch of positive returns since the global financial crisis, so we have to be ready to navigate some rough waters ahead."

Buckley, 48, who becomes Vanguard's fourth CEO, joined Vanguard as assistant to founder John C. Bogle after he graduated from Harvard University in 1991, returning there for his M.B.A. in 1996. Buckley has been part of Vanguard's senior leadership since 2001, serving as chief investment officer since 2013. He was Vanguard's chief information officer from 2006 to 2012.

Buckley also chairs the board of trustees of Children's Hospital of Philadelphia, according to his LinkedIn profile.

McNabb, 60, presided over Vanguard's efforts to expand its advisory business, urging customers to buy other Vanguard funds in addition to its popular low-fee stock and bond index funds, and expanded its Exchange-Traded Fund (ETF) business into one of the nation's largest. The company has also faced a string of state and federal tax challenges, which remain unresolved.

After the 2008 financial crisis, Vanguard attracted massive amounts of new assets linked to passive, or "indexed," mutual funds, and its low fees prompted a cost-cutting race between Vanguard and competitors such as BlackRock, Charles Schwab, and State Street.

In addition, dozens of Vanguard employees have sued since the early 2000s, saying they had been dismissed unfairly, prompting Vanguard to sweeten its severance and benefits packages under McNabb's reign.

"Bill [McNabb] will remain as chair," spokesman John Woerth said. "He will also serve as an ambassador with Vanguard clients both here and abroad. In addition, he expects to spend some time on policy matters, while continuing on the speaking circuit on investment and governance matters. On the personal side, he will stay involved with his nonprofit activities, including the Philadelphia Zoo."

McNabb "deftly" ran the firm through the market collapse of the late 2000s "into an era of unprecedented growth and global expansion," while adding a "deep bench" as he expanded the management team in recent years, said the company's lead independent board trustee, Mark Loughridge, a retired IBM chief financial officer said, in a statement.

Davis ran Vanguard's investment operations in the Asia-Pacific region before taking over the fixed-income group in 2014. He has an M.B.A. in finance from the Wharton School at the University of Pennsylvania and graduated from Pennsylvania State University. He is a CFA charter holder and a member of the CFA Society of Philadelphia.

"We are fortunate to have Greg at the helm of our global investment teams and as a new member of our senior leadership team," McNabb said. "His experience as a portfolio manager and as a leader of investment management teams, long-term orientation, and exceptional judgment make him an excellent steward of our clients' assets."

Besides the change in the top job, Vanguard says it will ask fund shareholders to approve its current board trustees and add two new ones — Sarah Bloom Raskin, former deputy secretary of the U.S. Treasury under President Barack Obam, and  Deanna Mulligan, chief executive of Guardian Life Insurance Co. of America.

"Vanguard's board and officers are beginning to reflect their consumer base – finally," said Dan Wiener, co-editor of the Independent Adviser for Vanguard Investors as well as CEO of Adviser Investments, which manages $5 billion for individuals and institutions. He also called Davis "very smart. I've heard him speak, and he's going to contribute a lot."

Vanguard's board will have four women out of 12 independent board members. Vanguard also introduced new language this year in its proxy statement that members of the board of trustees serve until they turn 72 years old, at which point they would step down, according to a proxy released Thursday, July 13.

As of June 2017, Vanguard managed 369 funds and served more than 20 million investors worldwide.