Colchian Dragon

In Ancient Greek mythology, Colchian Dragon was the guardian beast of a sacred grove to Ares in Colchis. It came into being after Typhon's blood was spilled when it fought Zeus. As the blood soaked into soil, Gaia was impregnated and gave birth to Colchian Dragon.

Description
If spread out, the dragon was said to be longer than a fifty oared longship. It guarded Golden Fleece, a great treasure for Colchians. Dragon was well fit for this task: it didn't need to sleep, nor could it die, and it was ever vigilant to the extent of never even blinking it's eyes. It was able to breathe fire.

Some of the dragons in Greek mythology have magical teeth that can be sown as seeds. From those seed emerge fully grown warriors along with their weapons. Colchian Dragon's teeth had this property.

Depending on source, Colchian Dragon was either slain by Jason or put to sleep by Medeia when they were on a mission to steal the Golden Fleece.

Trivia

 * In the famous 1963 adaptation of Jason of the Argonauts, the Colchian Dragon is substituted for the Hydra although the planted teeth still create warriors, famously in the form of skeletons.