Tiamat

Tiamat is the goddess of chromatic dragons. Like her counterpart Bahamut, she was a titan first called into being as a heavenly mount for the gods, but broke through her reins and became too powerful for even the gods to control.
Her avatar is that of an enormous five-headed dragon, with each head corresponding to one type of chromatic dragon (red, blue, black, green, and white, in that order). A single destructive breath from any of her heads is enough to obliterate an army in one fell swoop.