Hyder Ali, sultan of Mysore, born in Dina-velli, Mysore, about 1718, died Dec. 7,1782. He was of Arabian descent, and son of a petty chief. Entering the service of the rajah of Mysore in 1749, he rose in the course of ten years to be commander of the forces, and, having thus the power in his own hands, set aside the rajah with a pension of three lacs of rupees, and took possession of the sovereignty. The East India company, becoming alarmed at his increasing power, formed an alliance with the Mahrattas and the nizam of the Deccan against him; but Hyder not only gained over the nizam to his side, but for two years waged vehement war on the British. By a series of skilful manoeuvres he managed to draw their force to a distance from Madras, and then at the head of 6,000 horsemen rode 120 m. in three days and appeared before the city. The outlying country being at his mercy, the government of the presidency was compelled to come to terms, and Hyder agreed to a treaty of which the principal feature was that the British should form an alliance with him in his defensive wars. In 1770, the Mahrattas having invaded his dominions, he applied to the British for their promised aid, but could obtain from them nothing more than neutrality.

By the year 1778 he had recovered from the disadvantages their defection had caused him. Being once more threatened by the same warlike people, he again invited British assistance, hut with a like result. Incensed by this conduct, he formed an alliance with the Mahrattas and the nizam, and in 1780 invaded the British territory of the Carnatic, which he ravaged with fire and sword, capturing many of the strong places, but avoiding battle in the open field. The desolation he brought on the country during the two years' war was such that the British force, and even the city of Madras, were in danger from famine. This war elicited a remarkable display of military talent by the British general Sir Eyre Coote on the one side, and by Hyder and the French officers, of whom he had many in his service, on the other. The Mysore leader had already rejected terms of adjustment offered by Lord Macartney, the governor of Madras, when he died, and was succeeded by his son Tippoo Saib.