Mal-Ra and Orn-Ra are the Primordial sigils, representing the beginning and the end.
They pre-date all other sigils, and their existence is only recorded inside a book known as the Tome of Al-Mortagar. In order to contain their power, their stones must be carved out of Dakocite.
Their power is never fully revealed. The sigils are able to drain the life force out of other creatures, and can cause massive earthquakes, even summoning lava from the depths of RaDos.