Probably the most menacing presence in the movie, Dragon is the Fitzgibbons' cat – if “cat” is a strong enough word to describe him. To his family, he's a somewhat lazy mouser. To the rats of NIMH and the animals living in the field of the Fitzgibbons farm, he is a ravenous terror and a nigh-unstoppable force of nature. Whenever the rats venture beyond their secret colony on their various endeavors, they must first slip a sleeping drug concocted by Mr. Ages into Dragon's food dish – an act which cost the life of Jonathan Brisby (and perhaps others).  As for the mice and any other creatures unfortunate enough to catch his eye, there's only one option: run.

Origins of the character: In Robert C. O'Brien's book "Mrs. Frisby And The Rats Of NIMH", Dragon is described, at least physically, somewhat differently than he appears in the movie, though his menacing personality is pretty much the same: "The cat: He was called Dragon.  Farmer Fitzgibbon's wife had given him the name as a joke when he was a small kitten pretending to be fierce.  But when he grew up, the name turned out to be an apt one.  He was enormous, with a huge, broad head and a large mouth full of curving fangs, needle sharp.  He had seven claws on each foot and a thick, furry tail, which lashed angrily from side to side.  In color he was orange and white, with glaring yellow eyes, and when he leaped to kill, he gave a high, strangled scream that froze his victims where they stood."

In the animated sequel: Dragon does not make an appearance in the sequel.