A reconstruction of a heavy cavalryman of the Korean tribal union Gaya, ca. 4th cent CE, in an uknown Korean museum. He is protected by a full-body lamellar armour. Note the ‘opening’ of his armour around his waist in order to help him ride, and also his

unique lamellar “trousers”. He is armed with a sword. Behind him there is an image of a statuette depicting a Gaya heavy cavalryman on his horse. Note that the horse is also covered by a full-body lamellar armour.
Below, a map of Korea in 300 CE in which Gaya is noted among the other leagues and kingdoms on the southern end of the peninsula (wikimedia commons).