Doug Darling, executive director of the state’s main agency for job creation, resigned abruptly from his own job this week, six months after Gov. Rick Scott appointed him.

In a concise letter to Scott, Darling said Thursday he was leaving his post as executive director of the Department of Economic Opportunity for “personal reasons” and that his last day would be Tuesday.

The circumstances surrounding Darling’s resignation were still unclear Friday, and lawmakers said they had no reason to expect the sudden departure.

“My experience with Doug Darling has always been positive and professional,” said Sen. Don Gaetz, R-Niceville, who passed legislation last year creating the agency. “I was surprised to learn of it.”

Darling’s office faced some criticism in November after it released several documents indicating private businesses had failed to create thousands of promised jobs, despite receiving financial incentives over the past 15 years. Additionally, some information had been omitted from the release, and lawmakers and media outlets had requested more details.

Darling, 58, did not respond to calls seeking comment. Cynthia Lorenzo, director of the state’s Agency for Workforce Innovation, has been named interim director of DEO.

A month ago, the department released its first annual report on economic development, as well as a detailed study of the state’s multimillion-dollar business incentive program. That report, published by DEO’s private-business partner, Enterprise Florida, sought to clear up misconceptions about the original release.

Gray Swoope, president of Enterprise Florida, has spent the last few days responding to legislators who expressed concerns about the return on investment of the state’s incentive dollars. He acknowledged that some of the companies failed to create the jobs they had promised, but said those businesses had returned money to the state.

“In business, it’s hard to predict where you’re going to be in six years on a job projection, on investment projection or on wage protection,” he told a group of business leaders Thursday during an Enterprise Florida board meeting. “And if you miss one of those thresholds, by the way the laws are set, then the [incentive] program stops.”

Sen. Paula Dockery, R-Lakeland, who has been critical of state incentive programs in the past, said Darling had been trying to bring some accountability to the practice.

“He was trying to be more transparent about what deals had worked and had not,” she said. “I’d hate to think that was the reason he was let go.”

A retired high-ranking member of the U.S. Marine Corps, Darling has spent 15 years working in several positions in state government, including inspector general for the Department of Environmental Protection and chief of the state Division of Accounting and Auditing under former Chief Financial Officer Alex Sink.

Scott released a statement Friday thanking Darling for his work.

“I appointed Doug in July to lead the new agency, and I thank him for his invaluable efforts in getting DEO off the ground,” he said. “He has been a tremendous asset during these first months of the agency and has been instrumental in promoting Florida as the top place to do business.”

Darling is the third high-ranking member of Scott’s office to resign in the past year, following the departures of Corrections Secretary Ed Buss and Secretary of State Kurt Browning.

Darling had originally told Scott he would lead DEO through the 2012 lawmaking session. He said he would be available to help with the department’s transition until Feb. 29.

Until a permanent director is named, Lorenzo will lead the department as it navigates its first legislative term and launches a five-year economic development plan.

Gaetz said he hoped the governor would take this opportunity to appoint a business professional to lead the state’s economic development effort.

The ideal candidate, Gaetz said, is “an individual who knows how businesses operate and can talk peer-to-peer with business leaders about what’s necessary for the state to do for businesses to keep jobs, expand jobs and bring new jobs to the state of Florida.”