In Ezra 4: 7 etc. the reference is probably to Artaxerxes I, king of Persia 465–424 BCE, whose appointment of Nehemiah as governor in Jerusalem was probably to assist his ambitions against Egypt.
Citation for Artaxerxes
Citation styles are based on the Chicago Manual of Style, 15th Ed., and the MLA Style Manual, 2nd Ed..
MLA
"Artaxerxes." In A Dictionary of the Bible. Ed. W. R. F. Browning. Oxford Biblical Studies Online. Jun 18, 2013. <http://www.oxfordbiblicalcstudies.com/article/opr/t94/e162>.
Chicago
"Artaxerxes." In A Dictionary of the Bible. , edited by W. R. F. Browning. Oxford Biblical Studies Online, http://www.oxfordbiblicalcstudies.com/article/opr/t94/e162 (accessed Jun 18, 2013).