After the death of Kutubuddin Aibek, Illtumish threw out Kutubuddin`s weak son Aram within a year and took over the rule of his kingdom. He was also known as Illtumish.

Most of the Muizzi and Kutbi amirs (those created by Ghori and Kutbuddin) did not like the succession of Illtumish as he was only `the slave of a slave` and had rapidly risen from very humble beginnings to the position of the foremost amir under Kutbuddin. But Illtumish quickly overcame all those opposition from the nobles of Delhi and expanded his authority as far as the Siwalik Mountains on the one side and Benares on the other.

Kutubuddin Aibek`s next great task was the suppression of Eldoz who had established his power firmly in the Punjab. Illtumish defeated Eldoz near the fateful field of Tarain in 1215 A. D. and imprisoned him. Later, he put Eldoz to death to death shortly. By 1217 A.D., he drove out Kubaicha from the Punjab, though he continued to give trouble for a few more years. Kutubuddin Aibek`s next danger was a threatened irruption of the Mongol groups under the dreadful Chengiz Khan, the curse of the World. The Mongols continued to be a source of great threat to the north-western border and of considerable anxiety to the rulers of Delhi for years. Illtumish refused to give protection to the monarchs, who escaped from the attack of Chengiz Khan and kept himself safe from it. Illtumish emerged uninjured, and even triumphant, from this turmoil. The Mongols did not advance east of the Indus, fearing the heat of the country.

Illtumish now became strong enough to defeat his remaining rivals. In 1225 he secured the submission of Ghiyasuddin Khilji, the unruly governor of Bengal, who had invaded Jajnagar (in Orissa), Kamrup, Assam and Tirhut (North Bihar) and was exercising independent control. After two years, Illtumish sent another expedition under his son to punish the governor of Bengal and put down the nobles who had resisted the authority of Delhi. Another expedition followed this one. After some time, he overran Sind and brought about the fall of Kubaicha who was drowned in the Indus in the course of his flight from the Illtumish`s victorious army.

Illtumish then led expeditions into Malwa and Bundelkhand. The strong fortress of Ranthambhor was captured by him in 1226 A.D. The forts of Gwalior and Ujjayini and the temple of Mahakal were also destroyed mercilessly. He secured the popular diploma of investiture, as the Sultan of India in 1228 from the Caliph of Baghdad, who though powerless was still the high pontiff of Islam. This legitimised the position of Illtumish and greatly increased the prestige of the Indo-Muhammadan government in India. This was an historical event in Illtumish`s life as it silenced those who challenged Illtumish`s claim to the throne. Afterwards, Illtumish struck coins bearing his usual titles and in addition the proud legend, `Aid of the Commander of the Faithful`. He first introduced a purely Arabic coinage in India and adopted it as his standard coin. It was the `silver tanka` (the ancestor of the modern rupee) weighing 175 grains.

In this way, Illtumish brought under his control almost the whole of Hindustan except a few remote regions. It was he who should be regarded as the real founder of the Slave Dynasty and the consolidator of the kingdom of Delhi.

Illtumish was an indomitable warrior and was engaged throughout his reign in military projects. But he also managed to find some time to encourage the learned and the holy. He was a devout Mussalman and is credited with having built the Kutub Minar at Delhi, `whose massive majesty and beauty of design are unrivalled and which still stands as a living memorial to his greatness. The strong rule of Illtumish lasted for twenty-six years. He is regarded as the greatest of all the Slave kings and he added to the dominions of his predecessor the provinces of Sind and Malwa. Illtumish achieved all by himself and in the face of great odds. He was also noted for his extravagant generosity.