Dragon
Fiction
Animated continuity
At least one full-on dragon (reptilian, fire-breathing, winged) has been seen on Earth in medieval times, and a similar but less imposing creature (supposedly from Borneo) in the modern era. The medieval dragon was tremendous in size, dwarfing both humans and averaged-sized Transformers. Although quite dangerous, it was driven off by a wizard using dragon's bane. The modern creature was captured by Lord Chumley and used against the also-captive Optimus Prime. The creature was a little larger than Prime, had no wings, and never breathed fire. It attacked him with teeth and claws, but Prime threw it off a bridge.
Also, the fictional movie monster Hojoni bears a striking resemblance to the medieval dragon, though wingless.
The only known instance of a non-Terran dragon was in the dimension of Menonia, where a wizard called the Golden One could use magic to take on the form of a large, flying golden dragon.
Beast Wars
When the Predacon Megatron took on the spark of his Decepticon namesake and was submersed in lava, his form mutated from a Tyrannosaurus rex to a large, red, fire-breathing dragon. Whether this has any connection to the existence of actual dragons on Earth is unclear.
