|Dalwai of Mysore (de facto ruler)|
|Birthplace||Budikote, near Kolar in present-day Karnataka|
|Died||6 December 1782|
|Place of death||Chittoor|
|Predecessor||Krishnaraja Wodeyar II|
|Royal House||Sultanate of Mysore|
Hyder Ali (Urdu: ur, Kannada: ಹೈದರಾಲಿ, Haidarālī; Hindi: हैदर अली, Haidar Alī; c. 1720 – 7 December 1782, 2 Muharram 1197 in the Islamic calendar) was the de facto ruler of the Kingdom of Mysore in southern India. Born Hyder Naik, he distinguished himself militarily, eventually drawing the attention of Mysore's rulers. Rising to the post of dalwai, or commander-in-chief to Krishnaraja Wodeyar II, he came to dominate the titular monarch and the Mysore government, and eventually seized control of all of the reins of power. He expanded the kingdom's borders at the expense of the Maratha Empire and Nizam of Hyderabad (among others), and was one of the few local rulers to effectively blunt the military advances of the British East India Company during two wars. In the First and Second Anglo-Mysore Wars he came within striking distance of the British outpost at Madras. He was given a number of honorific titles, and was referred to as Sultan Hyder Ali Khan or Hyder Ali Sahib.
Hyder's rule of Mysore was characterised by frequent warfare with his neighbours and rebellion within his territories. This was not unusual for the time, as much of the Indian subcontinent was then in turmoil, with the Hindu Maratha Confederacy struggling with the remnants of the Muslim Mughal Empire. He was a shrewd leader, and left his son Tipu Sultan a kingdom that was significantly larger than when he first took it over. He organised his military in part along European lines, and was a pioneer in the military use of rocket artillery. He had at least two wives, and fathered at least three children.