Gert Rosenthal Königsberger (born 11 September 1935) is a Guatemalan diplomat.
He was born in Amsterdam to a German father and Guatemalan mother and came to Guatemala at the age of three. After secondary education in Guatemala, he studied in the United States and received a BA and an MA in economics from the University of California at Berkeley. He then pursued further studies in economics at San Carlos University in Guatemala City.
He entered government service in 1960 as a part-time economist at the National Planning Secretariat. In 1964 he was appointed representative of Guatemala on the Executive Council of the Central American Common Market, rising to Assistant to the Secretary-General of the Common Market's Secretariat in 1967. Between 1969 and 1970 he headed the National Planning Secretariat, a ministerial-level position. In 1971 he was named a fellow at the Adlai Stevenson Institute for International Affairs in Chicago, United States. Between 1972 and 1973 he directed a project in Guatemala for the United Nations Conference on Trade and Development, intended to promote the Central American Common Market. In 1973-74 he again headed the National Planning Secretariat
Between 1974 and 1985 he was the Director of the Mexico-based subregional office of the United Nations Economic Commission for Latin America and the Caribbean (ECLAC). In 1985, was promoted to Deputy Executive Secretary at ECLAC's headquarters in Santiago, Chile, and, in 1988, to Executive Secretary, with responsibility for the entire Latin America and Caribbean region.
In 1998 he was a member of the Oversight Commission of the Guatemalan Peace Accords. In 1999 he was appointed Permanent Representative of Guatemala to the United Nations, where he remained until 2004. In August 2006, following the resignation of Jorge Briz, President Óscar Berger appointed him Minister of Foreign Affairs, a position where he remained until the end of Berger's term on 14 January 2008. In April 2008 he was re-appointed Permanent Representative of Guatemala to the United Nations. In 2011, Guatemala was selected for a two-year rotating term in the UN Security Council. Guatemala was unanimously supported for this role and many UN officials saw this as a recognition of Gert Rosenthal as among the most respected diplomats at the UN. In October 2012, he was the President of the United Nations Security Council.