Ardashir I (died 242 AD) was the founder of the Sassanid Empire, was ruler of Istakhr (since 206?), subsequently Fars Province (since 208?), and finally "King of Kings of Sassanid Empire " (after 226) with the overthrow of the Parthian Empire. The dynasty founded by Ardashir would rule for four centuries, until it was overthrown by the Rashidun Caliphate in 651.

Ardashir (Arđaxšēr from Middle Persian and Parthian Artaxšaθra, Pahlavi ʼrthštr, "Who has the Divine Order as his Kingdom") is also known as Ardeshīr-i Pāpagān "Ardashir, son of Pāpağ", and other variants of his name include Latinized Artaxares and Artaxerxes.
Ardeshir was born in the late 2nd century in Istakhr, what is present-day Fars in Iran,[1][2] He was the son of Babak (Papak or Pabag) and Princess Rodak Ardashir is said to have ruled the town of Darabgerd and received the title of "argbadh". Upon Pāpağ's death, Ardashir's elder brother Šāpūr ascended to the throne. However, Ardashir rebelled against his brother and took the kingship for himself in 208.

Most scholars have assumed that Ardashir's father was Papak, a vassal king, and his grandfather was Sasan. However, there is another theory of his lineage, which is found in the Middle Persian book Book of Deeds of Ardeshir Son of Papak. This story is later confirmed by Ferdowsi's Shahnameh. This theory suggests that Sasan married the daughter of Papak after the latter discovers that Sasan is of royal Achaemenid descent. Hence Ardashir was born. From here onwards Sasan disappears from the story and Papak is considered the father. Ardashir helped Papak conquer some parts of Fars. It is possible that after Papak's death, his son Shapur, had a short reign which was probably ended by an accidental death. Around 211/12 Ardashir became ruler of Papak's kingdom, which was confined to central Fars. Soon he extended his realm into Kerman to the east and Elymais to the west, and demanding fealty from the local princes of Fars and gaining control over the neighboring provinces of Kerman, Isfahan, Susiana, and Mesene.[3]

This expansion came to the attention of the Arsacid Great King, Artabanus IV, who ordered his vassal, the ruler of Khuzestan, to confront Ardashir. It was Ardashir, however, who emerged victorious in that battle.[4] In 226, Artabanus IV himself invaded Fars to defeat the rebelling Ardashir. The latter won the first battle, but with heavy losses on both sides. In the second battle, the Parthians suffered a greater loss, and Ardashir was again deemed the victor. Their armies clashed once again in a final battle at Hormizdeghan, near the modern city of Bandar Abbas. At this encounter, the Parthian army was completely defeated, and Artabanus IV was killed. According to one account, Ardashir and Artabanus fought in close combat on horseback. Ardashir pretended to flee, turned around in the saddle and shot Artabanus through the heart.[5]

According to the hagiographic Book of the Deeds of Ardashir son of Babak, Ardashir I then went on to capture the western vassal states of the now-defunct Arsacid Empire.

Crowned in 226 as the Šāhān šāh Ērān "king of kings [of] Iran"[6] (his consort Adhur-Anahid took the title "Queen of Queens"), Ardashir finally brought the over 400 year-old Parthian Empire to an end and began four centuries of Sassanid rule.

Over the next few years, Ardashir I further expanded his new empire to the east and northwest, conquering the provinces of Sistan, Gorgan, Khorasan, Margiana (in modern Turkmenistan), Balkh, and Chorasmia. Bahrain and Mosul were also added to Sassanid possessions. Furthermore, the Kings of Kushan, Turan, and Mekran recognized Ardashir as their overlord. In the West, assaults against Hatra, Armenia and Adiabene met with less success.
According to historian Arthur Christensen, the Sassanid state as established by Ardashir I was characterized by two general trends which differentiated it from its Parthian predecessor: a strong political centralization and organized state sponsorship of Zoroastrianism.
War with Rome