Short answers, pulled from the story.
Hans Louis Trefousse (the 18th of December 1921 - the 8th of January 2010) was a German-American historian specializing in the Reconstruction Era and World War II. He was a professor at Brooklyn College from 1950 to 1998 and authored more than twenty books, with The Radical Republicans: Lincoln's Vanguard for Racial Justice (1969) considered by many historians his most influential work.
Trefousse emigrated from Germany in 1935 at age thirteen because his parents fled the increasingly totalitarian Nazi regime. He was born in Germany on the 18th of December, 1921, and the family settled in the United States before he completed his education.
Trefousse served in the U.S. Army as an intelligence officer, using his fluent German to interrogate captured German soldiers. He participated in the Liberation of Paris and, in Leipzig, spent eleven hours persuading a Nazi commander to surrender to Allied forces, saving hundreds of lives.
In The Radical Republicans: Lincoln's Vanguard for Racial Justice (1969), Trefousse argued against the dominant historical narrative of his time, contending that Reconstruction was a failed attempt to bring racial justice to the South rather than a corrupt imposition on the region.
After his first book on German and American neutrality, Trefousse encountered racist incidents in New York City that prompted him to change focus. His response was a 1957 biography of Benjamin Butler, the Union military governor of New Orleans, beginning a career-long examination of Reconstruction and its key figures.
Trefousse gained media attention during Bill Clinton's impeachment by drawing comparisons to Andrew Johnson's impeachment in the nineteenth century. His expertise derived from decades of scholarship, including his 1975 book Impeachment of a President: Andrew Johnson, the Blacks, and Reconstruction.