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, He was the son of Babak (Papak or Pabag) and Princess Rodak, descendant of the Shabankara tribe. According to a letter from Ardavan V, Ardashir was of Kurdish descent. 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.