Please answer the following question: Information: - Mark William Lippert (born February 28, 1973) is a U.S. public servant who was the United States Ambassador to South Korea from 2014 to 2017. Prior to his tour as Ambassador, Lippert had served as Chief of Staff for Secretary of Defense Chuck Hagel, Chief of Staff for the National Security Council, and Assistant Secretary of Defense for Asian and Pacific Security Affairs in the Department of Defense. On March 5, 2015, he was attacked by a man wielding a knife in South Korea. - The current United States Ambassador to South Korea is Mark Lippert . The ambassador 's official title is '' United States Ambassador to the Republic of Korea . '' - The United States Ambassador to South Korea is the chief diplomatic representative of the United States accredited to the Republic of Korea. The position of is currently vacant, but Marc Knapper, formerly Deputy Chief of Mission under the previous Ambassador Mark Lippert, is serving as Charge dAffaires until a new ambassador is confirmed. The ambassador's official title is "Ambassador Extraordinary and Plenipotentiary of the United States of America to the Republic of Korea." - Charles Timothy "Chuck" Hagel (; born October 4, 1946) is an American politician who served as a United States Senator from Nebraska from 1997 to 2009 and as the 24th United States Secretary of Defense from 2013 to 2015 in the Obama administration. Given the paragraphs above, decide what entity has the relation 'instance of' with 'position'.
Answer:
united states ambassador to south korea