| Walter Christian Ploeser | |
| State: | Missouri |
| District: | 12th |
| Term Start: | 3 January 1941 |
| Term End: | 3 January 1949 |
| Predecessor: | Charles Arthur Anderson |
| Successor: | Raymond W. Karst |
| Ambassador From2: | United States |
| Country2: | Paraguay |
| Term Start2: | 6 November 1957 |
| Term End2: | 12 September 1959 |
| Predecessor2: | Arthur A. Ageton |
| Successor2: | Harry F. Stimpson, Jr. |
| President2: | Dwight D. Eisenhower |
| Ambassador From3: | United States |
| Country3: | Costa Rica |
| Term Start3: | April 27, 1970 |
| Term End3: | April 13, 1972 |
| Predecessor3: | Clarence A. Boonstra |
| Successor3: | Viron P. Vaky |
| President3: | Richard Nixon |
| Office4: | Member of the Missouri House of Representatives |
| Term4: | 1931–1932 |
| Birth Date: | 7 January 1907 |
| Birth Place: | St. Louis, Missouri |
| Death Place: | St. Louis, Missouri |
| Nationality: | American |
| Party: | Republican |
| Spouse: | Dorothy Mohrig |
Walter Christian Ploeser (January 7, 1907 – November 17, 1993) was a U.S. Representative from Missouri and United States Ambassador to Paraguay and Costa Rica.
Born in St. Louis, Missouri, Ploeser attended the public schools of St. Louis, Missouri, Casper and Lusk, Wyoming, and the City College of Law and Finance, St. Louis, Missouri.He engaged in the insurance business in St. Louis, Missouri, in 1922 and founded his own company in 1933.Organizer and chairman of the board of Marine Underwriters Corp. 1935.He served in the State house of representatives in 1931 and 1932.
Ploeser was elected as a Republican to the Seventy-seventh and to the three succeeding Congresses (January 3, 1941 – January 3, 1949).He served as chairman of the Select Committee on Small Business (Eightieth Congress).He was an unsuccessful candidate for reelection in 1948 to the Eighty-first Congress.He served as delegate, 1964 and 1968 Republican National Conventions.He resumed the insurance business.He served as director of Webster Groves Trust Company.Ambassador to Paraguay in 1957–1959.He served as chairman of board, The Salvation Army from 1967 to 1969.Ambassador to Costa Rica in 1970–1972.He was a resident of St. Louis, Missouri, until his death on November 17, 1993.