A concept artist named Kimberley Pope worked on Seasons 1 and 2. From Season 3 onward, the task fell to karakter, a German studio who also do concept art for games like Black Ops III, Killzone, and Ryse. Artist Kieran Belshaw also worked on Seasons 5 to 7. The art that they all created was truly epic, and the show wouldn't exist without it. Check it out: