Lucius Quintus Cincinnatus Lamar (September 17, 1825 – January 23, 1893) was an American politician and jurist from Mississippi. A United States Representative and Senator, he also served as United States Secretary of the Interior in the first administration of President Grover Cleveland, as well as an Associate Justice of the U.S. Supreme Court. During the American Civil War, he participated in the Confederate government, briefly leading a volunteer regiment, and serving on diplomatic missions to Europe. James Longstreet was his cousin.
However, Lamar was part of a delegation of Congressmen and Senators that Lee had invited to examine the captured Rivington Men's headquarters in Richmond after the Richmond Massacre occurred on March 4, 1868. There Lee had laid out captured reference books and other documents for the delegation to examine. Lamar became convinced that Lee's position was correct but was reluctant to backtrack on a position he had run on until Judah Benjamin pointed out that his constituents could be swayed if he tied this to the reputation of the Rivington Men and the atrocities they had committed.
Longstreet was quite confident in Lamar's ability to deal with the Confederacy's European allies. However, he also realized that Lamar was not supportive of Longstreet's plans for manumission of the slaves.