William Slade was the White House usher, which at the time was "one of the highest posts available to a black Washingtonian"; he acted as valet, confidential messenger, doorkeeper, and majordomo to Abraham Lincoln, and remained in charge of the White House after Lincoln died.
Not who you're looking for? Others named William Slade: American politician (1786-1859) · British tug of war competitor (1873-1941)