After the Ammons moved back to the United States, he secured a position with Lord, Day and Lord. He subsequently went to work at the law firm of Mayer, Brown and Platt. One of this firm's clients was the then small investment firm of Kohlberg, Kravis, Roberts & Co. (KKR). In 1983, following his legal work on a KKR deal (and his divorce from his first wife), Ammon was recruited by the private equity firm, which specialized in leveraged buyouts. Ammon served as an Associate at Kohlberg, Kravis, Roberts & Co. from 1984 to 1989 and as a General Partner from 1990 to 1992. He worked on many deals, notably the famous $31 billion RJ Reynolds/Nabisco takeover. He joined his colleagues in becoming a multimillionaire and was quoted numerous times in the book "". According to Russ Baker in the May 2002 issue of "Gotham", "He was along for the wild ride as KKR grew into one of Wall Street's most aggressive and storied leveraged buyout outfits."