Al-Mansour 1 was Abu Ja`far `Abdullah ibn Muhammad ibn Ali; he assumed the name al-Mansour and was the second Abbasid caliph, reigning from 754 to 775.

Al-Mansour 1 was the brother of Aboulabas (as-Saffah 1): Theoph. AM 6241 (Ἀβουλαβᾶς, καὶ μετ'ἐκεῖνον τῷ ἀδελφῷ αὐτοῦ Ἀβδελᾶ), Theoph. AM 6246 (Ἀβουλαβᾶς ... Ἀβδελᾶς, ὁ ἀδελφὸς αὐτοῦ and Ἀβδελᾶν, τὸν υἱὸν Ἀλίμ, ἀδελφὸν δὲ Σαλίμ). He is regularly called Abdelas (Abdullah) in Theophanes. Elder brother of `Abd `Allah Abu -'l-`Abbas (as-Saffah 1), he was named `Abd `Allah and also known as Abu Ja`far: Chron. 1234, §179 (p. 328) (`Abd `Allah his brother, who was older than him and who was called Abu Ja`far), §181 (p. 332) (`Abd Allah Abu Ja`far). It was he who besieged the town of Wasit and persuaded Ibn Hubayra 1 to surrender under a promise of safety, before having him murdered: Chron. 1234, §181 (p. 332). He was nominated to succeed his brother (as-Saffah 1) as caliph; in the meantime he was made governor of Mesopotamia: Theoph. AM 6241 (τὸν δὲ Ἀβδελᾶν, τοῦ Ἀβουλαβᾶς ἀδελφὸν ἀπ'ἐκείνου ἔχοντα τὸν κλῆρον τῆς ἐπὶ τῆς Μεσοποταμίας ἔταξαν), cf. Chron. 1234, §184 (p. 338) ("To Abu Ja`far he gave authority over Mesopotamia and Armenia"). At his brother's death (as-Saffah 1) he was in Mecca; he wrote asking Abu Muslim 1 to secure the position of caliph for him and hastened to Persia while Abu Muslim 1 dealt with resistance in Syria; when Abu Muslim 1 also turned against him, he managed to lull his suspicions and then executed him; his position as caliph was then secure: Theoph. AM 6246, cf. Chron. 1234, §184 (p. 339) (narrating his succession as caliph and ending with the murder of Abu Muslim 1), Mich. Syr. II 518.

In 757 al-Mansour 1 compelled Christian monks, hermits and pillar-dwellers to pay taxes, and he sealed the treasuries of churches and brought in Jews to sell off the contents: Theoph. AM 6249. In 758 through Sulayman 3 he executed the leaders of a magian group in Beroea and Chalcis: Theoph. AM 6250. In 761/762 (year 1073 Sel.) he "built a city on the Tigris above Ctesiphon and he called it Baghdad" and made his residence there; he also built the city of Rafikah near Callinicum: Chron. 1234, §185 (p. 340).

In 763 al-Mansour 1 suppressed a revolt by Basra and the Arabs of the desert: Theoph. AM 6255. This was a Shi`ite revolt, which began in 762, under two brothers, mentioned but not named in Theophanes; they were Muhammad "the Pure Soul" and his brother Ibrahim; see Shaban, Islamic History, A New Interpretation, pp. 14-15.

Al-Mansour 1 was the father of Muhammad, to whom he gave the name al-Mahdi (al-Mahdi 1); al-Mansour 1 contrived to have his son nominated as his successor and heir-apparent in place of Isa ibn Musa 1 in c.765: Theoph. AM 6256 (see Isa ibn Musa 1 and Moses 1). He removed crosses from churches and forbade all night services and the study of Scripture: Theoph. AM 6258. In 769 he issued regulations concerning beards and headwear; he also laid siege all summer long to Kamachon but could not take it: Theoph. AM 6261. In 773 he sent a large army to Africa under the command of Moualabitos 1; he also visited Jerusalem where he fasted and issued orders for Christians and Jews to be branded on the hand; this led to a flight of Christians to the Roman empire: Theoph. AM 6264. Al-Mansour 1 died in September 775 (in the same month as the emperor Constantine V, Konstantinos 7) and was succeeded as caliph by his son Madi (al-Mahdi 1): Theoph. AM 6267. He died after a reign of twenty-three years, and was succeeded by his son Mahdi (al-Mahdi 1): Chron. 1234, §186 (p. 340). He rebuilt Melitene and Theodosiopolis of the Armenians, placing garrisons in both: Mich. Syr. II 522. He died at Mecca in 1087 Sel. after reigning twenty-one years: Mich. Syr. II 527.

Abdelas is said to have succeeded Marwan 2 as ruler of the Arabs and to have ruled for twenty-one years: Const. Porph., DAI 22, 56ff. The successors of Marwan 2 were the first two Abbasid caliphs, as-Saffah 1 and al-Mansour 1, who were both called Abdullah and who have been conflated in this source.

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