Isaiah 45:1 calls King Cyrus of Persia “G-d’s Messiah” among other references to him:
כֹּֽה־אָמַ֣ר יְהוָה֮ לִמְשִׁיחוֹ֮ לְכ֣וֹרֶשׁ אֲשֶׁר־הֶֽחֱזַ֣קְתִּי בִֽימִינ֗וֹ לְרַד־לְפָנָיו֙ גּוֹיִ֔ם וּמָתְנֵ֥י מְלָכִ֖ים אֲפַתֵּ֑חַ לִפְתֹּ֤חַ לְפָנָיו֙ דְּלָתַ֔יִם וּשְׁעָרִ֖ים לֹ֥א יִסָּגֵֽרוּ׃
Thus saith the Hashem to His anointed, to Cyrus, whose right hand I have holden, to subdue nations before him, and to loose the loins of kings; to open the doors before him, and that the gates may not be shut.
Scholars date Isaiah to have lived around the mid-eighth century BCE, but Cyrus lived around 529 BCE (after Isaiah’s death). How could Isaiah know about him?
Inspired by this question.