Kroll (formerly Duff & Phelps) is an American multinational financial and risk advisory firm that has its headquarters in New York City. It was established in 1932 as Duff & Phelps. In 2018, Duff & Phelps acquired the original Kroll company, which had been founded in 1972. In 2021, Duff & Phelps decided to rebrand itself as Kroll, a process it completed in 2022.

Duff & Phelps was founded in 1932 by William Duff and George Phelps in Chicago to provide investment research. Since that time, the firm expanded into corporate finance and investment management, as well as credit rating. In 1979, Duff & Phelps expanded into investment management, creating what would become Duff & Phelps Investment Management Co. (DPIMC), which was spun off into its own company in 2009 and was no longer part of the main Duff & Phelps firm.

In 1984, the company was nearly acquired by Security Pacific Corp. in a $35 million transaction. However, the deal was called off in early 1985 by Security Pacific Corp. because of restraints put on the deal by the Federal Reserve Board, which would have precluded the company from issuing public credit ratings.

The company was acquired five years later, in 1989, in a $146 million management buyout. The buyout was backed by Freeman, Spogli & Co., a private equity firm that controlled approximately two-thirds of the company, and management and employees owning the remaining third of the company's equity. The transaction was highly leveraged, financed with 79% bank borrowings and 15% coupon high-yield bonds. The company was taken public for the first time in 1992 through an initial public offering of stock on the New York Stock Exchange.

By the mid-1990s, Duff & Phelps, which was operating as a publicly traded company, began to focus on its core investment management, financial advisory and corporate finance operations. As a result, in October 1994, the Duff & Phelps's credit rating business, Duff & Phelps Credit Rating Co., was spun off to its shareholders and listed on the New York Stock Exchange. In 2000, Duff & Phelps Credit Rating Co. was acquired by Fitch Group, which later eliminated the use of the Duff & Phelps name.

In 2004, Lovell Minnick Partners sponsored a management buyout of the company, the second time the company had undergone a leveraged buyout transaction, acquiring the company from its then owner, Webster Financial Corporation. As part of the transaction, the company was merged with Stone Ridge Partners, a middle-market investment banking firm. In 2005, the company raised equity from Vestar Capital Partners to support the company's acquisition strategy that included the purchase of Standard & Poor's Corporate Value Consulting business as well as Valuemetrics, a financial advisory firm specializing in valuation services founded in 1981. In 2006, it acquired specialty restructuring firm Chanin Capital Partners, LLC.^{[citation needed]}

In 2007, Duff & Phelps completed its second initial public offering raising $133 million and listing the company's shares on the New York Stock Exchange. The IPO provided a partial exit for its two private equity financial sponsors. Also in 2007, the firm formed a strategic alliance with Tokyo-based Shinsei Bank. The firm has continued its acquisition strategy acquiring Dubinsky & Co., a financial consulting company and Kane Reece Associates. In 2010, the firm acquired the consulting business of Dynamic Credit Partners, bringing specialized talent in complex fixed income securities analysis, valuation and litigation support.

After less than five years as a public company, Duff & Phelps again agreed to a take-private offer from private equity firms. On December 30, 2012, Duff & Phelps, announced that it had entered into an agreement to be acquired for approximately $665.5 million by a consortium, comprising controlled affiliates of or funds managed by The Carlyle Group, Stone Point Capital LLC, Pictet & Cie and Edmond de Rothschild Group.