Baphomet was an enormous, tattered creature, jet black, but seemingly with blood and innards composed of molten metal. He had large appendages protruding from his head which held him aloft.
Whether a creature cast from heaven, or a dark god brought back from the Crusades, nobody knows. What is known however, is that in gathering the Tribes of the Moon to himself in Midian, Baphomet was attempting to create an army to take back what had once been his.
During the destruction of Midian, Baphomet chose Cabal to lead the remnants of the Tribes of the Moon to a new home before the Tabernacle collapsed, presumably killing or destroying the leader of the Nightbreed.