In Ezra 1, the LORD stirred the spirit of which king to let the exiles rebuild the temple?

Answer: Cyrus

In his first year, Cyrus king of Persia proclaimed that God's people could go up to Jerusalem and rebuild the house of the LORD.

“In the first year of Cyrus king of Persia, to fulfill the word of the LORD spoken through Jeremiah, the LORD stirred the spirit of Cyrus king of Persia to send a proclamation throughout his kingdom and to put it in writing as follows:”— Ezra 1:1 (BSB)