Shapur I or also known as Shapur I the Great was the second Sassanid King of the Second Persian Empire. The dates of his reign are commonly given as 240/42 – 270/72, but it is likely that he also reigned as co-regent (together with his father) prior to his father's death in 242 (more probably than 240).

Shapur was the son of Ardashir I (r. 226–240 [died 242]), the founder of the Sassanid dynasty and whom Shapur succeeded. His mother was Lady Myrōd, who—according to legend—was an Arsacid princess. The Talmud cites a nickname for her, "Ifra Hurmiz", after her bewitching beauty.

Shapur accompanied his father's campaigns against the Parthians, who - at the time - still controlled much of the Iranian plateau through a system of vassal states that the Persian kingdom had itself previously been a part of. Before an assembly of magnates, Ardashir "judged him the gentlest, wisest, bravest and ablest of all his children" and nominated him as his successor. Shapur also appears as heir apparent in Ardashir's investiture inscriptions at Naqsh-e Rajab and Firuzabad. The Cologne Mani-Codex indicates that, by 240, Ardashir and Shapur were already reigning together. In a letter from Gordian III to his senate, dated to 242, the "Persian Kings" are referred to in the plural. Synarchy is also evident in the coins of this period that portray Ardashir facing his youthful son, and which are accompanied by a legend that indicates that Shapur was already referred to as king.

Cyrus II of Persia (Old Persian: Kuruš (c. 600 BC or 576 BC–530 BC), commonly known as Cyrus the Great, also known as Cyrus the Elder, was the founder of the Achaemenid Empire. Under his rule, the empire embraced all the previous civilized states of the ancient Near East, expanded vastly and eventually conquered most of Southwest Asia and much of Central Asia, parts of Europe and the Caucasus. From the Mediterranean sea and Hellespont in the west to the Indus River in the east, Cyrus the Great created the largest empire the world had yet seen. He also pronounced one of the first historically important declarations of human rights via the Cyrus Cylinder sometime between 539-530 BCE.

The reign of Cyrus the Great lasted between 29 and 31 years. Cyrus built his empire by conquering first the Median Empire, then the Lydian Empire and eventually the Neo-Babylonian Empire. Either before or after Babylon, he led an expedition into central Asia, which resulted in major campaigns that were described as having brought "into subjection every nation without exception". Cyrus did not venture into Egypt, as he himself died in battle, fighting the Massagetae along the Syr Darya in December 530 BC. He was succeeded by his son, Cambyses II, who managed to add to the empire by conquering Egypt, Nubia, and Cyrenaica during his short rule.