WASHINGTON -- The Nationals appointed Mike Rizzo as assistant general manager and vice president of baseball operations on Monday.

The Nationals now have three assistant general managers, including Bob Boone, who is the director of player development and Tony Siegle, who is involved in contract negotiations and is a specialist in rules interpretations.

Rizzo's primary role will be to get the best amateur players in the United States, Latin America, Japan and Korea.

"He is very aggressive, has great work ethic. He is tremendous on pitchers, hitters, he is tremendous on makeup and character. He jumped on board on our philosophy of trying to get the best players in the world," general manager Jim Bowden said.

Rizzo, 45, joins the Nationals after spending the previous seven seasons with the Diamondbacks, primarily as director of scouting. Under his watch, the Diamondbacks drafted Brandon Webb, Chad Tracy, Justin Upton and Stephen Drew. Rizzo, who spent time in the White Sox organization, also signed Frank Thomas to his first professional contract.

The Nationals also are planning to hire a director of professional scouting and director of international scouting. Dana Brown, who is listed as the scouting director in the Nationals' media guide, is now the director of amateur scouting and will report to Rizzo.

"I consider Dana one of the best scouting directors in the game. Dana is on board with the hiring of Mike Rizzo. He supported it and is all for it," Bowden said. "All we are trying to do here is win. The more good minds we have together, the faster and quicker we could make better decisions and ... build a championship baseball team, which is the direction that we are going in."