Pabag (Middle Persian: 𐭯𐭠𐭯𐭪𐭩, Pāpak/Pābag; New Persian: بابک Bābak) was an Iranian prince who ruled Istakhr, the capital of Pars, from 205 or 206 until his death sometime between 207 and 210. He was the father, stepfather, grandfather, or father-in-law of Ardashir I, the founder of the Sasanian Empire. He was succeeded by his eldest son, Shapur.

Pars (also known as Persis), a region in the southwestern Iranian plateau, was the homeland of a southwestern branch of the Iranian people, the Persians. It was also the birthplace of the first Iranian Empire, the Achaemenids. The region served as the center of the empire until its conquest by the Macedonian king Alexander the Great (r. 336–323 BC). Since the end of the 3rd or the beginning of the 2nd century BCE, Pars has been ruled by local dynasties subject to the Hellenistic Seleucid Empire. These dynasts held the ancient Persian title of frataraka ("leader, governor, forerunner"), which is also attested in the Achaemenid-era. Later, under the frataraka Wadfradad II (fl. 138 BC), Pars was made a vassal of the Iranian Parthian (Arsacid) Empire. The frataraka were shortly afterwards replaced by the Kings of Persis, most likely at the accession of the Arsacid monarch Phraates II (r. 132–127 BC). Unlike the fratarakas, the Kings of Persis used the title of shah ("king") and laid the foundations for a new dynasty, which may be labelled the Darayanids.

There are various different sources regarding the relationship between Pabag, Sasan, and the first Sasanian monarch, Ardashir I (r. 224–242). According to the Shahnameh ("The Book of Kings") by the medieval Persian poet Ferdowsi (d. 1020), Sasan was a descendant of the mythological Kayanian rulers Dara II, Dara I, Kay Bahman, Esfandiyar, and Vishtaspa. The claim of Sasan belonging to the Kayanian family was designed in order to justify that Ardashir was descended from the ancient Kayanian kings, who reflected memories of the Achaemenids.

Dara II, the last Kayanian king to rule before Alexander, is partly based on the last Achaemenid King of Kings, Darius III (r. 336–330 BC), whose empire was indeed conquered by Alexander's forces. A son of Dara II named Sasan (called "the elder") fled to India and lived there in exile until his death. He was survived by a son who was likewise named Sasan (called "the younger"), "which continued in the family for four generations". A descendant of the family, likewise named Sasan, worked for Pabag, who was a local ruler in Pars. Pabag's daughter married Sasan and bore him a son named Ardashir. Following this, Sasan is no longer mentioned. The Shahnameh thus indicates that the ancestors of Sasan resided in India following Alexander's conquests. This report has been used by scholars to point out Sasan's Indo-Parthian connection.

According to the medieval Iranian historian Al-Tabari (d. 923), Pabag was the son of Sasan and a princess named Rambihisht, who was from the Bazrangid family, a dynasty of rulers in Pars. He presents Pabag as the father of Ardashir. Like Ferdowsi in his Shahnameh, Al-Tabari also describes Sasan as a foreigner in Pars; however, unlike him, he does not mention Sasan's place of origins.

The Middle Persian text Kar-Namag i Ardashir i Pabagan ("Book of the Deeds of Ardashir, son of Pabag"), says the following regarding the ancestry of Ardashir: "Ardashir, the Kayanian, son of Pabag from the parentage of Sasan and from the lineage of King Dara". Another Middle Persian text, the Bundahishn, however, gives the genealogy of Ardashir as follows: "Ardashir son of Pabag whose mother was the daughter of Sasan son of Weh-afrid". This demonstrates the inconsistencies between Middle Persian texts regarding the origins of the Sasanian dynasty. Both sources regard Pabag as the father of Ardashir, while Sasan is presented as the latter's grandfather or ancestor.

In Roman and Armenian sources, a different account appears. According to the Roman historians Agathias and George Syncellus, Sasan was the biological father of Ardashir, while Pabag was his stepfather. The Armenian writers Movses Khorenatsi and Agathangelos likewise call Sasan the father of Ardashir. However, they do not make any mention of Pabag. A Greek variant of Agathangelos' work calls Ardashir "son of Sasanus, which is the origin of the Sasanian name of the Persian kings descended from him".

Ardashir, in his coin engravings and inscription on Naqsh-e Rostam, claims to be the son of "divine Pabag, the king". His son and successor, Shapur I (r. 240–270), on his inscriptions at Naqsh-e Rajab and Ka'ba-ye Zartosht, calls himself a son of Ardashir I and grandson of Pabag. Although various figures named "Sasan" are mentioned in the inscription, none of them are associated with the House of Sasan. The Paikuli inscription of Shapur I's son Narseh (r. 293–303), however, makes direct references to the House of Sasan, such as the phrase "since the gods gave glory and rulership to the family of Sasan", which indicates that Narseh saw Sasan as his ancestor.