It is by extreme the largest feathered dinosaur ever to have been unearthed and raises exciting questions as to why some of these crusty reptiles developed plumage.
Three nearly full skeletons of the dinosaur have been opened in beds of sediment in Liaoning province, northeastern China, scientists reported in Nature.
The soil has been old to around 125 million years ago to the mid-Cretaceous time, at the peak of the dinosaurs' long reign over the earth.
The new genus has been named Yutyrannus huali, and mixture of Latin and Mandarin which means "beautiful feathered tyrant."
"The feathers of Yutyrannus were simple filaments," said Xu Xing, a well-known fossil hunter from Beijing's institution of Vertebrate Palaeontology and Palaeoanthropology.
"They were additional like the fuzzy down of a recent baby chick than the stiff plumes of an adult bird."
The fossils contain element of the Yutyrannus tail and, most usefully, its skull.
They reveal the sharp teeth, three-fingered hand and pointed head of a typical theropod – a carnivore that walked on its hind legs.
At mature size, a Yutyrannus would have been about 30 feet long and weighed around 1.4 tons, with feathers at least six inches long.
That makes it a midget compared to its cousin T. rex but a massive compared to the Beipiaosaurus, the earlier plumed record-breaker, which was 40 times lighter.
Yutyrannus was too big to fly and in any case the feathers were too downy to even get it off the ground, says the document.
That raises the theory that the feathers evolved for padding at what was a curiously cool time of the long Cretaceous era.
But one more idea is that the feathers were there for display, as birds use them for mating purposes.
The almost complete skeletons came from the Yixian Formation in Liaoning, which has been a treasure trove of dinosaurs.
Discoveries there have bolstered the theory that birds nowadays are the descendants of tiny feathered theropods that took to the trees, either for food or safety, and then cultured to glide or fly.
"Yutyrannus dramatically increases the size variety of dinosaurs for which we have specific proof of feathers," Xu said.
"It's possible that feathers were a lot more widespread, at least among the meat-eating dinosaurs, than the majority scientists would have guessed even a few years ago."