Al-Mu`tasim 1 was known as Abu Ishaq ('bw shq) and was the brother of the caliph al-Ma'mun 1 (his predecessor): Chron. 1234 §213 (II, p. 24), §215 (II, p. 27), §216 (II, p. 28), cf. Mart. XLII Amor. (cited below; his name is given as Ἀβησὰκ). Uncle of Abbas 1: Chron. 1234, §213 (II, p. 24), §215 (II, p. 27), §216 (II, p. 28), §223 (II, p. 35). He was "Abu Ishaq, who was called al-Mutasim": Chron. 1234, §223 (II, p. 35). He was the father of his two successors as caliph, al-Wathiq 1 and al-Mutawwakil 1.

In c. 832 al-Mu`tasim 1 and Abbas 1 prepared to accompany al-Ma'mun 1 on an invasion of Byzantine territory, following the return of Manuel 1 to the service of the emperor Theophilos (Theophilos 5): Chron. 1234, §213 (II, p. 24). In the year 1144 Sel. (i.e. 833) al-Mu`tasim 1 and Abbas 1 led the vanguard of a large invasion force under al-Ma'mun 1: Chron. 1234, §215 (II, p. 27). After the death of al-Ma'mun 1 (on 23 July 833) the succession was disputed for a while between Abu Ishaq (al-Mu`tasim 1) and Abbas 1; eventually Abbas 1 gave his support to his uncle: Chron. 1234 §216 (II, p. 28).

Al-Mu`tasim 1 was caliph from 833 to 842. During the reign of Theophilos 5 he attacked and captured Amorion, sacking it and killing all there except the seven commanders of the themes, whom he took into captivity: Mart. XLII Amor., p. 1 (Ἀβησὰκ ἐκεῖνος ὁ πρωτοσύμβουλος τοῦ Ἰσμαηλιτῶν ἔθνους), p.42, p. 65, cf. pp. 11, 29 (ὁ βούλαρχος τῶν Ἀγαρηνῶν, brought Kallistos 2 to Syria and imprisoned him with the captives from Amorion), 44. Al-Mu`tasim 1 is the unnamed caliph whose native city of Sozopetra was sacked by the emperor Theophilos (Theophilos 5) in spite of his entreaties to desist: Theoph. Cont. III 29 (p.124) (πατρίδα ... τοῦ ἀμεραμνουνῆ), Zon. XV 29. 1 (πατρὶς ετύγχανε τοῦ ἀμερνουμνῆ). To take his revenge he mounted a great expedition against the Romans with the intention of capturing Amorion, home city of Theophilos 5: Theoph. Cont. III 30 (pp. 125-126), Zon. XV 29. 8-9. Having determined to attack Amorion he sent a section of his army under his son (sic; the commander was Afshin 1, who was not the son of al-Mu`tasim 1) together with the emir of Melitene, Amr 2, and the Turkish archers and all the Armenian troops to make trial of the strength of the emperor's forces; they defeated the emperor's army at the battle of Anzen near Dazemon: Theoph. Cont. III 31 (pp. 126-128) (unnamed; ὁ τῶν Σαρακηνῶν ... ἡγεμών). Both armies of the caliph (ὁ ἀμεραμνουνῆς) then united at Amorion and began the siege; al-Mu`tasim 1 refused all pleas from Theophilos 5 to withdraw, still angry at the earlier attack on his own birthplace: Theoph. Cont. III 33 (pp. 129-130), Zon. XV 29. 14-17.

Al-Mu`tasim 1's home town was Sozopetra, which was attacked by Theophilos 5; in revenge he attacked and captured the home town of Theophilos 5, Amorion, carrying off many distinguished captives: Genesius III 11. He rejected all Theophilos 5's attempts to ransom them: Genesius III 12. When his home town of Sozopetra was sacked (this is another account of these events) he assembled troops from Egypt and Palestine and sent them under his own son, with Besparakanites 1, the archon of archons (Anonymus 200) and Amr 2 the ruler of Melitene; they made camp at Dazymon: Genesius III 13. After the victory over Theophilos 5 at Anzes he united his forces with those of his son against Amorion: Genesius III 14 (called ὁ πρωτοσύμβουλος).

This campaign is recorded in the Syriac tradition. Abu Ishaq (al-Mu`tasim 1) divided his invading forces into two and gave one section to Afshin 1; with the other he himself crossed into Byzantine territory via Tarsos and laid siege to Ankara; Afshin 1 joined him after defeating Theophilos 5 and they captured and destroyed Ankara; they then marched to Amorion, laid siege to it and captured and destroyed it too: Chron. 1234, §§221- 222 (II, pp. 33-34). Al-Mu`tasim 1 then left Amorion and made his way to Baghdad, where report had it that Abbas 1 was planning a rebellion; he remained there "a short time of a year or more", then fell ill and died, in the year 1153 Sel. (i.e. 842); he was succeeded by his son Harun (al-Wathiq 1): Chron. 1234, §223 (II, p. 35), §226 (pp. 35-36).

Al-Mu`tasim 1 was the son of the caliph Mamun (al-Ma'mun 1), whom he accompanied on the expedition into Cilicia during which al-Ma'mun 1 died: Bar Hebr., p. 133. Brother (sic) of `Abbas (i.e. Abbas 1): Bar Hebr., p. 133, p. 138. He succeeded his father as caliph and reigned for eight years and eight months: Bar Hebr., p. 133. In the year 1147 Sel. (835/836) al-Mu`tasim 1 received the Nubian king Georgios 250 in Baghdad: Bar Hebr., pp. 134-135. He sent Afshin 1 with gifts for Stephanos 157 and seized and killed Babek (Babak 1): Bar Hebr., p. 136. In the year 1149 Sel. (837/838) al-Mu`tasim 1 invaded the lands of the Romans and also sent Afshin 1 with another army; he pulled down the walls of Nikaia and Ankyra, both abandoned by their inhabitants: Bar Hebr., p. 136. He besieged and captured the city of Amorion and caried off many of the inhabitants into captivity: Bar Hebr., pp. 136-138. He rejected peace overtures from the emperor Theophilos (Theophilos 5) after the capture of Amorion when his demands for the surrender of Nasr the Kurd (Theophobos 1) and Manuel the patrician (Manuel 1) were rejected; he ordered Abu Sa`id 1 and Bashir 1 to conduct raids into the lands of the Romans: Bar Hebr., p. 138. Later he made peace with Theophilos 5 and exchanged prisoners; the date was apparently in or after the year 1152 Sel. (840/841): Bar Hebr., p. 139. Al-Mu`tasim 1 died in the year 1154 Sel. (842/843), at about the same time as the emperor Theophilos 5: Bar Hebr., p. 140.

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