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Ameritrade Holdings

(AMTD) - Get Report

said Tuesday that its founder, J. Joe Ricketts, is immediately relinquishing his role as co-chief executive of the company, but will remain chairman as he prepares for his eventual retirement.

Ameritrade's other chief executive, Thomas K. Lewis, will take over all the responsibilities in that post. Lewis, a technology expert, was handpicked by Ricketts to help lead the company in March 1999, just as it was struggling with computer problems related to the explosive growth of its Internet brokerage service.

The executive reshuffling comes less than two months after Ameritrade named J. Randy MacDonald chief financial officer, replacing Robert Slezak, who retired in November.

The departure of Ricketts, 58, from Ameritrade's day-to-day operations is intended to allow him to focus on his personal interests. Over the next few years, he and his wife, Marlene, plan to liquidate their retirement accounts, and sell and donate about 20% of their family holdings. In an attempt to avoid flooding the market with stock, he plans to sell his 20 million shares of Ameritrade through private placements.

Shares of Ameritrade moved lower Tuesday amid weakness in the markets. In midmorning trading, the stock was down 1/8, or 1%, at 12 7/16. The stock has fared poorly in recent months, and is down from its high around 30 last November. (Ameritrade closed down 13/16, or 6%, at 11 3/4.)

Lewis has largely been credited with bolstering Ameritrade's presence in new technology platforms such as wireless devices, and increasing the speed and reliability of Ameritrade's Internet-based service.

"Tom has developed a management team that is best equipped to manage Ameritrade's growth in this highly competitive and rapidly changing industry," Ricketts said in a statement.

As he ascends to become the sole chief executive, Lewis plans to buy a large block of Ameritrade shares, in accordance with a recent change of policy at Ameritrade, which requires executives to hold a minimum level of company stock based on their base salary.

Before joining Ameritrade, Lewis was president of

TenFold Insurance Systems

, where he headed marketing, sales, consulting and business development. He was also a founder of

Seer Technologies

, helping to build the company into a global technology consulting firm.