(Reuters) - Duke Energy Corp
Duke CEO Jim Rogers, 64, will become CEO of the combined company, while remaining chairman, the company said.
Duke said the resignation of Johnson, 58, was by "mutual agreement."
The deal, first announced in January 2011, creates the largest U.S. power company with 7.1 million electricity customers in North Carolina, South Carolina, Florida, Indiana, Kentucky and Ohio, and 57,000 megawatts of generating capacity.
Ann Maynard Gray, Duke's lead director, said Johnson was "instrumental in helping us close the merger with Progress Energy, and we wish him well in his future endeavors."
Gray, on a conference call, declined to comment further about the executive change.
At least one analyst expressed concern Duke could lose senior executive at Progress, many of whom are loyal to Johnson.
Rogers said he contacted Progress executives Monday night "and talked through where we're going in the future and how we have to pull together.
"My expectation is that all will lead and make this a great success," Rogers said.
(Reporting By Michael Erman and Ernest Scheyder; Editing by Gerald E. McCormick and Maureen Bavdek)