A translation of a concept art page from Hyrule Historia. Images taken from History of Hyrule’s The Legend of Zelda art anthology.
The Ocean King
An illustration of the Ocean King, the true form of Oshus. His design is whale-themed. You can see this form of the Ocean King at the end of the game’s story.
Linebeck
Linebeck, with is brave smile. The face of descendent, Linebeck III, who appears in Spirit Tracks, looks identical to his. However, his clothes are slightly different.
Mutoh & The Spirits of the Cobble Knight Leaders
Below, we see King Mutoh, who dwells on the Isle of the Dead. We also see a spirit of one of the leaders of the Cobble Knights, who follow him. There are 3 of these in all. Each wears garb of different colours. The first is red, the second is green, and the third is yellow.
Translator’s Note: This paragraph is really confusing. According to Zelda Wiki, there are 4 Cobble Knights in all, not 3. The blue knight pictured isn’t mentioned.
Follower (Spirit Knight)
Kayo & Astrid
Astrid the Fortune Teller and her attendant, Kayo. Kayo’s design is pretty much identical to his appearance in the final game, but the colour of Astrid’s hair was altered, among other things.