MUNKAR and NAKIR منكر و نكمر
“The Unknown” and “The Repudiating.” The two angels who are said by Muhammad to visit the dead in their graves and to interrogate them as to their belief in the Prophet and his religion.
They are described as two black angels with blue eyes. (Mishkat, book I. ch. v.) [PUNISHMENTS OF THE GRAVE.]
Based on Hughes, Dictionary of Islam