David Lau, Jefferson National Financial’s chief operating officer, has vacated the post after nine years with the company, company officials confirmed today.

The company would not elaborate on the reasons for Lau’s departure.

Lau was one of the architects behind the company’s flagship product: the Monument Advisor variable annuity. The low-cost, flat-fee variable annuities were introduced in 2005 and have since helped the company win a sizeable following among fee-based registered investment advisors.

The company has come under pressure in recent years, however, as other annuity companies have duplicated the strategy to make inroads in the RIA market.

When Financial Advisor inquired about Lau’s departure, the company responded by e-mail with a statement that confirmed he was no longer with the company.

“The company is appreciative of his many contributions and wishes him well in his future endeavors,” the company said in the statement.

It provided no other details on Lau and the circumstances surrounding his departure. “As a matter of company policy, Jefferson National does not comment on personnel matters,” company spokeswoman Katherine Kilpatrick said in the e-mail.

Jefferson National did note in its statement, however, that its Monument Advisor product surpassed $2.5 billion in assets in the second quarter.

“The company continues to target $1 billion in sales for 2014, after topping $700 million in 2013 and $400 million in 2012,” the statement said. “We are very excited about the direction the company is taking and our prospects for the future, and look forward to continued success as we partner with fee-only and fee-based advisors across the U.S.”

As the company that introduced the flat-fee variable annuity to the marketplace, Jefferson National remains a formidable force in the RIA market. Barron’s, for example, named the company’s Monument Advisor the nation’s best variable annuity in June, noting its modest $240 annual fee.

At the same time, industry watchers have noted that there is now heated competition in the marketplace that Jefferson helped create, as investors scrounge for income as they flee the bond market. One of the emerging players in the market is Jackson National Life, which over the past six years has come out of nowhere to become the nation’s biggest seller of variable annuities, according to Morningstar. Spearheading Jackson’s growth has been a product called Elite Access, a variable annuity designed to combine low cost with a wide range of investment options.