King of Kings in the context of "Shapur II"

Darius I (Old Persian: 𐎭𐎠𐎼𐎹𐎺𐎢𐏁 Dārayavaʰuš; c. 550 – 486 BCE), commonly known as Darius the Great, was the third King of Kings of the Achaemenid Empire, reigning from 522 BCE until his death in 486 BCE. He ruled the empire at its territorial peak, when it included much of West Asia, parts of the Balkans (Thrace–Macedonia and Paeonia) and the Caucasus, most of the Black Sea's coastal regions, Central Asia, the Indus Valley in the far east, and portions of North Africa and Northeast Africa including Egypt (Mudrâya), eastern Libya, and coastal Sudan.

Darius ascended the throne after overthrowing the Achaemenid monarch Bardiya (or Smerdis), who he claimed was in fact an imposter named Gaumata. The new king met with rebellions throughout the empire but quelled each of them; a major event of Darius's career described in Greek historiography was his punitive expedition against Athens and Eretria for their participation in the Ionian Revolt.

Tigranes II, more commonly known as Tigranes the Great (Tigran Mets in Armenian; 140–55 BC), was a king of Armenia. A member of the Artaxiad dynasty, he ruled from 95 BC to 55 BC. Under his reign, the Armenian kingdom expanded beyond its traditional boundaries and reached its peak, allowing Tigranes to claim the title Great King or King of Kings. His empire for a short time was the most powerful state to the east of the Roman Republic.

Either the son or nephew of Artavasdes I, Tigranes was given as a hostage to Mithridates II of Parthia after Armenia came under Parthian suzerainty. After ascending to the Armenian throne, he rapidly expanded his kingdom by invading or annexing Roman and Parthian client-kingdoms. Tigran decided to ally with Mithridates VI of Pontus by marrying his daughter Cleopatra. At its height, Tigranes' empire stretched from the Pontic Alps to Mesopotamia and from the Caspian Sea to the Mediterranean. With captured vassals, his lands even reached the Red Sea and the Persian Gulf. Many of the inhabitants of conquered cities were forcibly relocated to his new capital, Tigranocerta. An admirer of the Greek culture, Tigranes invited many Greek rhetoricians and philosophers to his court, and his capital was noted for its Hellenistic architecture.

The Parthian Empire (/ˈpɑːrθiən/), also known as the Arsacid Empire (/ˈɑːrsəsɪd/), was a major Iranian political and cultural power centered in ancient Iran from 247 BC to 224 AD. Its latter name comes from its founder, Arsaces I, who led the Parni tribe in conquering the region of Parthia in Iran's northeast, then a satrapy (province) under Andragoras, who was rebelling against the Seleucid Empire. Mithridates I (r. c. 171 – 132 BC) greatly expanded the empire by seizing Media and Mesopotamia from the Seleucids. At its height, the Parthian Empire stretched from the northern reaches of the Euphrates, in what is now central-eastern Turkey, to present-day Afghanistan and western Pakistan. The empire, located on the Silk Road trade route between the Roman Empire in the Mediterranean Basin and the Han dynasty of China, became a center of trade and commerce.

The Parthians largely adopted the art, architecture, religious beliefs, and regalia of their culturally heterogeneous empire, which encompassed Persian, Hellenistic, and regional cultures. For about the first half of its existence, the Arsacid court adopted elements of Greek culture, though it eventually saw a gradual revival of Iranian traditions. The Arsacid rulers were titled "King of Kings", claiming inheritance of the Achaemenid Empire; indeed, they accepted many local kings as vassals, although the Achaemenids would have had centrally appointed, albeit largely autonomous, satraps. The court did appoint a small number of satraps, largely outside Iran, but these satrapies were smaller and less powerful than the Achaemenid potentates. With the expansion of Arsacid power, the seat of central government shifted from Nisa to Ctesiphon along the Tigris (south of Baghdad), although several other sites also served as capitals.

Darius III (Old Persian: 𐎭𐎠𐎼𐎹𐎺𐎢𐏁 Dārayavaʰuš; Ancient Greek: Δαρεῖος Dareios; c. 380 – 330 BC) was the thirteenth and last Achaemenid King of Kings of Persia, reigning from 336 BC to his death in 330 BC.

Contrary to his predecessor Artaxerxes IV Arses, Darius was a distant member of the Achaemenid dynasty. During his early career, he was reportedly an obscure figure among his peers and first rose to prominence during the Cadusian expedition of Artaxerxes III in the 350s BC. As a reward for his bravery, he was given the Satrapy of Armenia. Around 340 BC, he was placed in charge of the royal "postal service," a high-ranking position. In 338 BC, Artaxerxes III met an abrupt end after being poisoned by the court eunuch and chiliarch (hazahrapatish) Bagoas, who installed Artaxerxes' youngest son Arses on the throne. He only reigned for a few years, until Bagoas had him poisoned as well. Darius was subsequently installed on the throne and soon forced Bagoas to drink his poison after discovering that the eunuch had planned to poison him as well.

Khagan or Qaghan (Middle Mongol:ᠬᠠᠭᠠᠨ; Khaan or Khagan; Old Turkic: 𐰴𐰍𐰣 Kaɣan) is a title of imperial rank in Turkic, Mongolic, and some other languages, equal to the status of emperor and someone who rules a khaganate (empire). The female equivalent is Khatun.

It may also be translated as "Khan of Khans", equivalent to King of Kings. In Bulgarian, the title became known as Khan, while in modern Turkic, the title became Khaan with the g sound becoming almost silent or non-existent; the ğ in modern Turkish Kağan is also silent. After the division of the Mongol Empire, monarchs of the Yuan dynasty and the Northern Yuan held the title of Khagan. Kağan, Hakan and Kaan, Turkish equivalents of the title are common Turkish names in Turkey.

Arses or Arsaces (c. 445–359/8 BC), known by his regnal name Artaxerxes II (Old Persian: 𐎠𐎼𐎫𐎧𐏁𐏂 Artaxšaçāʰ; Ancient Greek: Ἀρταξέρξης), was King of Kings of the Achaemenid Empire from 405/4 BC to 359/8 BC. He was the son and successor of Darius II (r. 423 – 405/4 BC) and his mother was Parysatis.

Soon after his accession, Artaxerxes II faced opposition from his younger brother Cyrus the Younger, who assembled an army composed of troops from his Lydian and Ionian satrapies as well as Greek mercenaries in his bid for the throne. The forces of the brothers clashed at Cunaxa in 401 BC, which resulted in the defeat and death of Cyrus. Following this, Artaxerxes II had to contend with several other revolts; a revolt by Evagoras I (r. 411–374 BC) in Cyprus between 391–380 BC, by the Phoenicians in c. 380 BC, and most importantly, the revolts by the western satraps (known as the Great Satraps' Revolt) in the 360s and 350s BC, led by distinguished figures such as Datames, Ariobarzanes, and Autophradates.

Xerxes I (/ˈzɜːrksiːz/ ZURK-seez; c. 518 – August 465 BC), commonly known as Xerxes the Great, was a Persian ruler who served as the fourth King of Kings of the Achaemenid Empire, reigning from 486 BC until his assassination in 465 BC. He was the son of Darius the Great and Atossa, a daughter of Cyrus the Great.

In Western history, Xerxes is best known for his invasion of Greece in 480 BC, which ended in Persian defeat. Xerxes was designated successor by Darius over his elder brother Artobazan and inherited a large, multi-ethnic empire upon his father's death. He consolidated his power by crushing revolts in Egypt and Babylon, and renewed his father's campaign to subjugate Greece and punish Athens and its allies for their interference in the Ionian Revolt. In 480 BC, Xerxes personally led a large army and crossed the Hellespont into Europe. He achieved victories at Thermopylae and Artemisium before capturing and razing Athens. His forces gained control of mainland Greece north of the Isthmus of Corinth until their defeat at the Battle of Salamis. Fearing that the Greeks might trap him in Europe, Xerxes retreated with the greater part of his army back to Asia, leaving behind Mardonius to continue his campaign. Mardonius was defeated at Plataea the following year, effectively ending the Persian invasion.

Kavad I (Middle Persian: 𐭪𐭥𐭠𐭲 Kawād; 473 – 13 September 531) was the Sasanian King of Kings of Iran from 488 to 531, including a two or three-year interruption. A son of Peroz I (r. 459–484), he was crowned by the nobles to replace his deposed and unpopular uncle Balash (r. 484–488).

Inheriting a declining empire where the authority and status of the Sasanian kings had largely weakened, Kavad tried to reorganize his empire by introducing many reforms whose implementation was completed by his son and successor, Khosrow I. They were made possible by Kavad's use of the Mazdakite preacher Mazdak, leading to a social revolution that weakened the authority of the nobility and the clergy. Because of this, and the execution of the powerful king-maker Sukhra, Kavad was deposed and imprisoned in the Castle of Oblivion. He was replaced by his brother Jamasp. However, with the aid of his sister and an officer named Siyawush, Kavad and some of his followers fled east to the territory of the Hephthalite king, who provided him with an army. This enabled Kavad to restore himself to the throne in 498/9.

Khosrow I (also spelled Khosrau, Khusro or Chosroes; Middle Persian: 𐭧𐭥𐭮𐭫𐭥𐭣𐭩), traditionally known by his epithet of Anushirvan (Middle Persian: 𐭠𐭭𐭥𐭱𐭫𐭥𐭡𐭠𐭭, lit. 'the Immortal Soul'), was the Sasanian King of Kings of Iran from 531 to 579. He was the son and successor of Kavad I (r. 488–496, 498/9–531).

Inheriting a reinvigorated empire at war with the Byzantines, Khosrow I signed a peace treaty with them in 532, known as the Perpetual Peace, in which the Byzantine emperor Justinian I paid 11,000 pounds of gold to the Sasanians. Khosrow then focused on consolidating his power, executing conspirators, including his uncle Bawi. Dissatisfied with the actions of the Byzantine clients and vassals, the Ghassanids, and encouraged by Ostrogoth envoys from Italy, Khosrow violated the peace treaty and declared war against the Byzantines in 540. He sacked the major city of Antioch and deported its population to Persia. In 541, he invaded Lazica and made it an Iranian protectorate, thus initiating the Lazic War. In 545, the two empires agreed to halt the wars in Mesopotamia and Syria while continuing to fight in Lazica. A truce was declared in 557, and by 562 the fifty-year peace treaty was signed.