Saichania (Mongolian meaning "beautiful one") was an Ankylosaur from the Late Cretaceous Period. It was discovered in Mongolia, alongside the Tarbosaurus, Protoceratops, and Velociraptor. Saichania was over five metres long and weighed over two tonnes, making it somewhat big, although smaller than its more famous cousin, Ankylosaurus. It was more robustly built than other members of the Ankylosaur family. Its body was flat and low-slung, standing on four short legs. The forelimbs were very powerful. The head was protected by bulbous armour tiles. It could defend itself against predators like Tarbosaurus with a tail-club.
Wikipedia has a more detailed and comprehensive article on Saichania