The Black Titan was the former god of death, long before the Dead Flower, who was originally a follower of him, was introduced into the pantheon. He embodied many more aspects of death than she currently does, but upon his death, many of the gods took up his more important duties to continue the cycle of life and death. It's believed that the death of the Black Titan, at the hands of the Poisoner, was one of the many causes for the War of the Gods.
The Black Titan is depicted as a large, imposing figure, much larger than the other gods of the time, even the Harvest Bringer and the Morning Star. His skin is made of pure deathly energy, he is jet black with the only change in colour being his stark white eyes. Unlike the comforting hands of the Dead Flower, if you saw the Black Titan, you should be afraid of what was about to happen.