Pacific Investment Management Company, LLC (commonly called PIMCO), is an investment firm headquartered in Newport Beach, California. PIMCO is led by co-founder William H. Gross, (usually known as Bill Gross) who serves as Co-Chief Investment Officer, and Mohamed A. El-Erian, the other Co-CIO as well as the firm's CEO. It is the world’s largest bond investor.

Gross manages the Total Return Fund, the world’s largest mutual fund with assets of $242.7 billion as of June 30, 2011. He co-founded the firm in 1971, launching with $12 million of assets. Previously, PIMCO had functioned as a unit of Pacific Life Insurance Co., managing separate accounts for that insurer's clients. In 2000, PIMCO was acquired by Allianz SE, a large global financial services company based in Germany, but the firm continues to operate as an autonomous subsidiary of Allianz.

PIMCO oversees investments totaling more than $1.7 trillion on behalf of a wide range of clients, including millions of retirement savers, public and private pension plans, educational institutions, central banks, foundations and endowments, among others.

William Hunt "Bill" Gross (born April 13, 1944) is an American financial manager and investment author who co-founded Pacific Investment Management (PIMCO). Gross also runs PIMCO's $252.2 billion Total Return Fund.

Gross was born in Middletown, Ohio, the son of Shirley, a homemaker, and Sewell M. Gross, a sales manager for AK Steel Holding. He was raised a Presbyterian. His family moved to San Francisco in 1954. Gross graduated from Duke University in 1966 with a degree in psychology. At Duke he joined Phi Kappa Psi. He then served in the Navy and earned an MBA from the UCLA Anderson School of Management in 1971. Gross briefly played blackjack professionally in Las Vegas, Nevada, and has said that he applies many of his gambling methods for spreading risk and calculating odds to his investment decisions. He is also a CFA Charterholder, earning his credentials while working as an investment analyst for Pacific Mutual Life between 1971 and 1976.

Gross manages one of the world's largest mutual funds, focusing mostly on bonds. Called "the nation's most prominent bond investor" by the New York Times, he co-founded Pacific Investment Management (PIMCO) and currently manages PIMCO's Total Return fund (the world's largest bond fund and fifth largest mutual fund) and several smaller ones.