Turning a decapitated Celestial head into a forge, Knull created an army of symbiotes from his darkness and used them to conquer planets.
However, the symbiote-dragon was defeated by Thor on Earth and his lightning severed Knull’s connection to the symbiotes.
To fight them, Knull crafted a living sword called All-Black (which is a big part of a really good, but unrelated, Thor comic), but he eventually lost it.