List of ambassadors of the United States to Mexico
List of ambassadors

Ambassador
Presentation
Termination
Appointed by
Powell Clayton
January 3, 1899
May 26, 1905
William McKinley
Edwin H. Conger
June 15, 1905
August 3, 1905
Theodore Roosevelt
David Eugene Thompson
March 8, 1906
December 1, 1909
Theodore Roosevelt
Henry Lane Wilson
March 5, 1910
February 18, 1913
William Howard Taft
Henry P. Fletcher
March 3, 1917
January 25, 1919
Woodrow Wilson
Charles B. Warren
March 31, 1924
July 22, 1924
Calvin Coolidge
James R. Sheffield
October 15, 1924
June 5, 1927
Calvin Coolidge
Dwight Morrow
October 29, 1927
September 17, 1930
Calvin Coolidge
J. Reuben Clark
November 28, 1930
February 14, 1933
Herbert Hoover
Josephus Daniels
April 24, 1933
November 9, 1941
Franklin D. Roosevelt
George S. Messersmith
February 24, 1942
May 15, 1946
Franklin D. Roosevelt
Walter C. Thurston
June 17, 1946
November 4, 1950
Harry S. Truman
William O'Dwyer
November 23, 1950
December 6, 1952
Harry S. Truman
Francis White
April 28, 1953
June 30, 1957
Dwight D. Eisenhower
Robert C. Hill
July 25, 1957
December 1, 1960
Dwight D. Eisenhower
Thomas C. Mann
May 8, 1961
December 22, 1963
John F. Kennedy
Fulton Freeman
April 6, 1964
January 6, 1969
Lyndon B. Johnson
Robert H. McBride
July 22, 1969
January 25, 1974
Richard Nixon
Joseph J. Jova
January 30, 1974
February 21, 1977
Richard Nixon
Patrick Joseph Lucey
July 19, 1977
October 31, 1979
Jimmy Carter
Julian Nava
May 7, 1980
April 3, 1981
Jimmy Carter
John Gavin
June 5, 1981
June 10, 1986
Ronald Reagan
Charles J. Pilliod Jr.
November 4, 1986
April 7, 1989
Ronald Reagan
John Negroponte
July 3, 1989
September 5, 1993
George H. W. Bush
James R. Jones
September 10, 1993
June 25, 1997
Bill Clinton
Jeffrey Davidow
August 5, 1998
September 14, 2002
Bill Clinton
Tony Garza
November 22, 2002
January 20, 2009
George W. Bush
Carlos Pascual
August 9, 2009
March 19, 2011
Barack Obama
Earl Anthony Wayne
August 2, 2011
July 31, 2015
Barack Obama
Roberta S. Jacobson
June 20, 2016
May 5, 2018
Barack Obama
William H. Duncan
2018
-
Donald Trump

Question: Who did Truman appoint as US Ambassador to Mexico in 1950 and how long did they serve in that role?
Answer: Harry Truman appointed William O'Dwyer as U.S. Ambassador to Mexico in 1950, who served until 1952.