Bill Thompson, co-CEO of Pacific Investment Management Company, is planning to step down at the end of the year, placing Mohamed El-Erian, who has the deeper investment background, in sole control of the bond investing giant.

El-Erian and Thompson have been co-CEOs since El-Erian returned to PIMCO in January. With both sharing responsibilities, PIMCO has charted an aggressive expansion strategy, including entering the exchange-traded funds market. (See related story.)

It has been a busy few years for El-Erian. He was recruited away from PIMCO two years ago by Harvard University to run its $35 billion endowment fund, when famed Harvard manager Jack Meyer left to start a hedge fund. Managing the mega-endowment was a job El-Erian did well, before ultimately deciding to return to PIMCO: The Harvard endowment returned 23% during 2007, its best return in seven years. El-Erian originally joined PIMCO in 1999 as a managing director and senior member of the PIMCO portfolio management and investment strategy group. El-Erian was also given the position of co-chief investment officer with Bill Gross, upon his return to PIMCO. He will remain co-CIO with Gross, in addition to his CEO duties, according to a statement from the company.

El-Erian comes out of a deep global investing background, whereas Thompson's strength was as a corporate officer, helping to grow PIMCO from its early days as a niche bond investing shop into the fund industry powerhouse that it is today. Maybe most notable during Thompson's CEO tenure was the engineering of the deal for PIMCO to be acquired by German financial services giant Allianz in 2000. Under Thompson, PIMCO grew from $40 billion in assets under management to its present size of $835 billion.

El-Erian's global background comes from a combination of his personal history and investment industry experience. He was raised the son of an Egyptian diplomat and is fluent in Arabic, French and English. He served as deputy director at the International Monetary Fund and as a managing director of Salomon Smith Barney in London, before joining PIMCO in 1999.