Northern Ireland's US economic envoy has resigned.
Declan Kelly has helped to create 1,500 jobs since his appointment in September 2009 by US Secretary of State Hillary Clinton.
Major American companies such as the New York Stock Exchange, Euronext, Citi and Kana Software have brought employment to Northern Ireland.
Mrs Clinton said: "During his time as envoy, Declan has helped our friends in the Northern Ireland Executive and Assembly, Invest NI, and the business community make Northern Ireland one of the best per capita attractors of investment in the world."
She added: "The United States will continue to work with Northern Ireland to expand the opportunities Declan has fought so hard for, and I know he will remain a passionate advocate for the people of Northern Ireland."
Mr Kelly, 43, who was born in Portroe, Co Tipperary, in the Irish Republic, helped Londonderry become UK City of Culture 2013. The married father-of-two co-ordinated the Clinton Global Initiative session on Northern Ireland economic opportunities in 2009 and the US-Northern Ireland economic conference in 2010.
First Minister Peter Robinson said: "The assistance and advice that Declan has provided has been invaluable as we have set about the task of rebalancing Northern Ireland's economy. In recent times we have created more jobs than ever before at a higher level than ever before. Declan has worked closely with Invest NI to help make this happen."
Deputy First Minister Martin McGuinness said: "Declan Kelly has been a great friend of the peace process and has played a key role in helping the executive attract increasing levels of inward investment over the past couple of years.
"He played a significant part in helping key companies such as Citi, NYSE Euronext, Terex, Dow Chemical to locate or expand their presence here and we owe him a huge debt of gratitude."
Nationalist SDLP leader Margaret Ritchie said the US should remain focused on Northern Ireland investment. "Attracting foreign direct investment remains key to the economic recovery of the north and I would urge the US administration to demonstrate that their commitment will remain undiminished in the wake of Mr Kelly's departure," she said.