The sword has an edge capable of cutting through anything but its most distinctive feature is that it is semi-alive, with a mind of its own, and feeds on souls. The blade's nominal "owner", the albino prince Elric of Melniboné, loathes the sword, but is dependent on it for the strength and vitality it gives him. The sword's hunger for souls is such that it frequently betrays him, turning in his hands and killing friends and lovers, adding to Elric's self-loathing as he feels their stolen strength and souls flooding into himself.
Books by Moorcock about Stormbringer:
The band Hawkwind, who have had a long association with Moorcock, released an entire album about the story of Elric and Stormbringer, The Chronicle of the Black Sword (1985). The song Black Blade by Blue Oyster Cult is about Stormbringer.