Tughril Beg led the Seljuk Turks from steppe clan to Middle Eastern empire: victor of Dandanaqan (1040), master of Baghdad (1055), and the first Turk invested by the caliph as sultan.
Tughril and his brother Chaghri led the Seljuk branch of the Oghuz across the Oxus in the 1020s as hired swords and hungry migrants; at Dandanaqan in 1040 they broke the Ghaznavid empire's field army and divided eastern Islam between them — Chaghri taking Khurasan, Tughril the westward road.
The road ended at Baghdad. In 1055 the powerless Abbasid caliph invited him in against the Shia Buyid emirs; in 1058 al-Qa'im crowned him "King of East and West" — the caliphate's spiritual authority now wedded to Turkish military power. The bargain defined Sunni statecraft for centuries, and made the Turks, within one generation of paganism, Islam's swordarm.
Tughril was born about 990 into the ruling kin of the Seljuk Oghuz, in the steppe world north of the Aral Sea; the clan had lately converted to Islam, a decision that pointed its raids and its loyalties south. Orphaned early, he and Chaghri were raised by their grandfather Seljuk himself in the tradition's telling.
The brothers' early decades were the freelance politics of the frontier: service and betrayal among Qarakhanids and Khwarazmians, imprisonments, escapes, and at last the fatal invitation into Khurasan, where the Ghaznavid sultan Mas'ud alternately settled and massacred the hungry Turkmen until the quarrel came to battle.
The Muslim chroniclers, Ibn al-Athir foremost, wrote Tughril as the acceptable face of the Turkish conquest: patient where his Turkmen were rapacious, abstemious, regular in prayer, famously clement at Baghdad where his troops' entry had begun in riot. The praise is formulaic in places, but the career it decorates — half a century without a recorded act of gratuitous cruelty to a surrendered enemy, in that century — gives it substance.
His statecraft had a steppe chieftain's patience and a convert's calculation: twenty years pacing the conquest of Persia city by city, the Shia Buyids dismantled under a Sunni-restoration banner that cost nothing and bought legitimacy everywhere, and at the end the extraordinary demand — pressed to the point of scandal and granted on his deathbed's eve — to marry the caliph's own daughter: the nomad's blood joined to the Prophet's house.
Dandanaqan (May 1040) was the founding act: three days of thirst-war outside Merv destroyed Mas'ud of Ghazna's great army, and the brothers' famous division followed — Chaghri the east, Tughril the west, the empire run as a family federation, with all its future civil wars implicit. Tughril took Nishapur, then Rayy and Isfahan through the 1040s and 1050s, sending the unruly Turkmen ahead into Armenia and Anatolia — the raids that Byzantium would meet at Manzikert a generation later.
Baghdad crowned the design. Entering in December 1055 as the caliph's deliverer from the Buyids, he survived the Basasiri revolt that briefly restored Shia prayers in the capital (1058–1060), restored al-Qa'im, and received the double investiture: sultan, "King of East and West", with his name in the khutba beside the caliph's. Church and sword had found their Sunni constitutional form: the caliph reigned, the sultan ruled.
Tughril's sultanate became the template of Middle Eastern government for half a millennium: Turkish military dynasties ruling in the caliph's name — Seljuks, Zengids, Ayyubids, Mamluks, Ottomans — all descend constitutionally from the investiture of 1058. The Turkmen pressure he aimed westward reshaped Anatolia permanently within thirty years of his death.
He died childless at Rayy in 1063; the empire passed, after a short convulsion, to Chaghri's son Alp Arslan, and then to Malik-Shah — the three-reign arc that contemporaries already recognised as the Great Seljuk age. His tomb tower at Rayy, a plain brick cylinder of enormous dignity, still stands over the city's traffic.