Kokkos (or Kokkos of Nicea, Kokkos, the Astronomer) was one of the Founders of Kitezh. He is - among others - mentioned in the Document Kokkos, the Astronomer from The Prophet's Trail set and in the inscription Kokkos, the Astronomer on the Mural in his Crypt.
Of his life, not much is known. He was "branded a heretic in his home city" and left the Byzantine Empire together with the Prophet. His knowledge of the stars helped them to plot a course north and made sure they arrived safely. He is said to have often had philosophical discussions with the Prophet about "the nature of the universe" and man's place in it. For the prophet he build the Orrery.
From his name "Kokkos of Nicea" we can deduce that he was born in or around that city. "Nicea" might be a different spelling for "Nicaea", the modern city of Nice in France. Note that this is nowhere confirmed within the game.