A very long time ago, the greedy dwarfs lived inside their mountains, digging deeper and deeper for riches.
Some say dwarfs were once giants living above ground, tall and skinny as pine trees, but as they dug closer to the centre of the earth, gravity reshaped their bodies along the way. When the pressure became too high, their bodies finally gave in and the dwarfs popped like bubbles. All that remained was their black blood, filled with powerful greed, and it filled every hole and crevice deep down in the mountainside.
But this was a long time ago. Nowadays, the crazed orks drill everywhere for this black gold, hoping to pump some fuel for their strange machines and devices of war and destruction. Some say it's even good for your skin.