It is estimated that in 480 B.C. the Persian (Achaemenid) empire had 50 million people living until its control. This huge amount was roughly 44% of the world's population at the time, making it the largest world power ever in terms by population percentage.
Cyrus the Great (559 - 530 B.C.)
Cyrus conquered the Medians in 549 and the Babylonians in 539. Cyrus is considered the founder of the Persian (Achaemenid) empire and its first true ruler. King Cyrus was known as a "singularly noble and just monarch." One of his first acts, after gaining control of Jews held in Babylonian captivity, was to authorize their return to Jerusalem (2Chronicles 36:22 - 23).
Cambyses II (530 - 522 B.C.)
Son of Cyrus the Great.
Bardiya (522 B.C.)
Son of Cyrus the Great and brother of Cambyses II. He likely ruled the empire for only a few months in 522.
Darius I the Great (522 - 486 B.C.)
Under Darius the rebuilding of Jerusalem's temple resumes and is completed (Ezra 6:15). The Persian (Achaemenid) empire, under his reign, reaches its peak in power and land controlled.
Xerxes I the Great (485 - 465 B.C.)
Son of Darius I. Ahasuerus (Xerxes in the Greek), the Persian (Achaemenid) King named in the book of Esther (Esther 1), was likely Xerxes I.
Artaxerxes I (464 - 424 B.C.)
Son of Xerxes I. Artaxerxes authorized his cupbearer, Nehemiah the prophet, to rebuild Jerusalem's walls.
Xerxes II (424 B.C.)
Son of Artaxerxes.
Sogdianus (424 - 423 B.C.)
Son of Artaxerxes.
Darius II Nothius (423 - 405 B.C.)
Son of Artaxerxes.
Artaxerxes II (404 - 359 B.C.)
Son of Darius II, Artaxerxes II is considered the longest reigning Achaemenid ruler.
Artaxerxes III (358 - 338 B.C.)
Son of Artaxerxes II.
Artaxerxes IV Arses (337 - 336 B.C.)
Son of Artaxerxes III.
Darius III (336 - 330 B.C.)
Darius III is the great-grandson of Persian (Achaemenid) King Darius II. He was the last king of the empire. He was defeated by Alexander the Great in 331 B.C. at the battle of Arbela near Nineveh. Persia, after this defeat, subsequently falls and Alexander captures Babylon.