The firm that made index funds fashionable will get its fourth CEO in its four-decade history.

Vanguard Group will get its fourth chief executive since it was founded four decades ago.

Current chairman and chief executive William McNabb will step down as CEO in January and be succeeded by long-time company insider Mortimer J. Buckley.

Buckley, 48, who goes by the name Tim, was named president and director as part of the succession plan, the company announced Thursday. He has been the fund firm’s chief investment officer. McNabb, 60, will continue to remain at the company as chairman after he hands the CEO reins over in January.

Vanguard, based in Malvern, Pa., is one of the world’s biggest fund managers, with $4.4 trillion in assets. Its founder, John Bogle, popularized the concept of low-cost index fund investing. That philosophy has caught fire in recent years with a proliferation of index-tracking funds and trendier exchange traded funds. Much of the investor money has come Vanguard’s way. Assets under management were about $1 trillion shortly after McNabb took the helm in 2008.

In a statement on Thursday, he said “it is the right time for a new leader and the Board is unanimous in its belief that Tim Buckley is the ideal next chief executive.”

Buckley joined Vanguard’s top executive ranks in 2001 and has been chief investment officer since 2013. Greg Davis, 46, who is global head of fixed income, was named chief investment officer to succeed him.

When he first started working at Vanguard in 1991, Buckley worked as assistant to then-chairman Bogle, according to the company’s statement.