Who to sacrifice to get the ebony mail?

To obtain the Ebony Mail in "The Elder Scrolls V: Skyrim," you must sacrifice an NPC named Hrolfdir. He can be found during the quest "The Black Star" in the quest line related to the Daedric Prince Boethiah. Once you have the Ebony Mail, you will be rewarded with the armor piece, which provides stealth and damage resistance benefits.