Дарий I
Darius I was the obvious King at the time of Haggai and Zechariah as the statements made of "These seventy years" from Zechariah 1:12 refer to exactly seventy years from the 6th year of Darius I, when the 2nd Temple was completed, which when counted inclusively, from the destruction of Jerusalem in 587 B.C equals exactly seventy years.