Haidar Ali, the ruler of the Kingdom of Mysore in southern India, became a dead enemy of the British primarily because they did not help him against the Marathas.

Supporting Point: Background on Haidar Ali's rule in Mysore
- Haidar Ali, a military leader and administrator, rose to power in Mysore in the mid-18th century.
- He modernized the Mysorean army and implemented administrative reforms, making Mysore a formidable power in southern India.

Supporting Point: The British and their interests in India
- The British East India Company had established its presence in India and was expanding its influence and control over various parts of the country.
- They had established settlements and trading posts along the Indian coastline, including Madras (present-day Chennai).

Supporting Point: Haidar Ali's conflicts with the Marathas
- The Marathas, another powerful Indian empire, posed a threat to Haidar Ali's rule in Mysore.
- In an attempt to expand his territories and counter the Marathas, Haidar Ali sought assistance from the British.

Supporting Point: British refusal to help against the Marathas
- Despite Haidar Ali's request for assistance, the British did not provide any substantial help in his conflict with the Marathas.
- The British had their own strategic interests and did not see it as beneficial to get involved in Haidar Ali's conflicts.

Supporting Point: Haidar Ali's resentment towards the British
- Haidar Ali perceived the British refusal to help as a betrayal and a lack of loyalty.
- This created a deep animosity towards the British, as he had expected their support against a common enemy.

Supporting Point: Haidar Ali's subsequent actions against the British
- Frustrated by the British, Haidar Ali turned his attention towards them and started attacking their settlements and trading posts, including Madras.
- He formed alliances with other regional powers, including the French, to counter British influence.

Conclusion:
Haidar Ali's resentment towards the British stemmed from their refusal to help him in his conflict with the Marathas. This refusal led to his perception of betrayal, and he subsequently became a dead enemy of the British, launching attacks against their settlements and forming alliances against them.