It is an artifact of the Daedric Prince Mephala. The Ebony Blade is a Daedric artifact found during the quest The Whispering Door. Warhammers are, hands down, the strongest out of all the two-handed weapons in the Skyrim world. This Daedric artifact has been around Tamriel for hundreds of years and it can often be found across the eras, which explains why it is seen in almost every single TES title.
Two of these Daedric quests involve the reward being a choice between two artifacts, one quest being the 'The Black Star' and the other being. Before these artifacts can be obtained, however, specific tasks called Daedric quests must be performed. Of the seventeen Daedric Princes, sixteen have an artifact attributed to them in The Elder Scrolls V: Skyrim.
