Samuel Beckwith

Captain Samuel H. Beckwith (December 18, 1837 – 6 December 6, 1916) was a telegraph and cipher officer to Ulysses S. Grant. He was nicknamed "Grant's Shadow" by other staff officers. Beckwith was the first to transmit news of John Wilkes Booth's whereabouts after Lincoln's assassination, leading to his capture. Beckwith was also present as Grant's telegraph officer on Abraham Lincoln's visits.
In Washington, Lincoln used to daily visit the telegraph office, and cipher operator David Homer Bates was later to recall these visits, along with the testimony of Thomas T. Eckert, Charles A. Tinker, Albert B. Chandler, and Albert E. H. Johnson in Lincoln in the Telegraph Office (1907).

In the 2012 film Lincoln, the character of the Washington war-room telegraph officer is credited as Grant's officer "Samuel Beckwith" but appears to be based on the memoirs of Washington cipher officer David Homer Bates. He was played by Adam Driver.