Adam Badeau was a pretty good writer, a New York theater critic before the Civil War and the author of several books afterward. During the war, he became a staff officer to an obscure general and was seriously wounded in Louisiana in 1863. He recovered at the home of his friend, the famous actor Edwin Booth, in company with Booth's brother and fellow actor John Wilkes, the future assassin, while the New York City draft riots raged outside.
Then Badeau got a job on Grant's staff, and for the next couple of decades derived most of his income from the federal government in jobs arranged by Grant. Then -- as the Grants saw it -- while helping the general prepare his Memoirs, he betrayed him and the whole family at their hour of greatest need.
Despite the aforementioned limitations of biography, someone should write one of Badeau. Meanwhile, I couldn't get rid of him even after Grant did, and he winds up with the final word in The Last Circle of Ulysses Grant.