Diamat is the French name of the Pokemon Zweilous, though the name origin for that Pokemon is slightly different. Coincidentally, both Pokemon are Dragon-types whose names reference Tiamat.
Design origin[]
Diamat is based on Western dragons and diamonds. Diamonds are formed by carbon being highly compressed in the Earth's mantle. However, the idea that diamonds are formed from compressed coal is a common misconception, though it is certainly possible for that to happen in rare circumstances.
Name origin[]
Diamat's name is a combination of diamond and Tiamat, the name of a Mesopotamian sea serpent and ocean goddess. The idea of Tiamat as a dragon goddess specifically arose in part because of the deity of the same name in the tabletop roleplaying game Dungeons & Dragons.