Whisper Man

 were a group of faceless men, who were with The Great Intelligence at the The Doctor's Tomb.

Biology
It is unknown what exactly they are made of, seeing as Strax sliced one of them, and then it was rebuilt. They also have the function to reach into people's hearts, to kill them. They also know how to get from place to place, being able to teleport to Earth and Trenzalore. (TV: The Name of the Doctor).

History
The Whisper Men were unknown, and could get from place to place, quickly. They killed Jenny Flint when she was in dream state, and almost killed Clara Oswin Oswald, Madame Vastra and Strax too at Trenzalore, in order for The Doctor to tell his name, with The Great Intelligence's orders. when the Intelligence went into the time wound and made all The Doctor's victories into defeats, the men disappeared from the TARDIS. (TV: The Name of the Doctor).