A considerable number of mythological deities are said to throw thunderbolts - Zeus and Thor are merely the most familiar of these to Europeans, with examples known from many other cultures. Actual mythic creatures that throw lightning, however, are much less common, although Chinese dragons are at least associated with thunder and storms. In D&D, however, it seems an obvious attack mode once we've dealt with fire and ice, and, naturally enough, it's associated with the dragon that's the colour of the sky.1E
The original picture of the blue dragon shows an animal with a moderately long and heavy snout, large eyes, and elongated canine teeth. More distinctive features include the fact that the dorsal frill of the green and black dragons is here replaced with a series of large triangular plates, which may be projections from the vertebrae, but could be separate structures similar to those on a Stegosaurus. The latter possibility is supported by the existence of three similar plates on the forehead. In front of these, there is a row of four bony spikes, one of which is enlarged to form a narrow nasal horn. As usual, this doesn't look like it would be of much use in combat, at least compared to the teeth and claws, so it might be a display structure.
