The correct answer is option 'C', Mir Jafar.

Mir Jafar was a military general and the commander-in-chief of the Nawab of Bengal, Siraj-ud-Daulah. He played a significant role in the Battle of Plassey, which took place on June 23, 1757.

The Battle of Plassey:
The Battle of Plassey was a crucial event in the history of colonial India. It was fought between the forces of the British East India Company, led by Robert Clive, and the army of Siraj-ud-Daulah, the Nawab of Bengal.

Background:
Siraj-ud-Daulah was the ruler of Bengal, Bihar, and Orissa and had a strained relationship with the British East India Company. He became suspicious of their intentions and tried to assert his authority by imposing restrictions on their trade and fortifications. This led to tension between Siraj-ud-Daulah and the British.

Mir Jafar's Betrayal:
Mir Jafar, who was initially a loyal general of Siraj-ud-Daulah, secretly conspired with the British to overthrow the Nawab and secure his own position. He was dissatisfied with Siraj-ud-Daulah's rule and saw an opportunity to gain power and wealth by collaborating with the British.

The Role of Mir Jafar in the Battle:
Mir Jafar played a crucial role in the Battle of Plassey. He deliberately weakened Siraj-ud-Daulah's forces by withdrawing his troops from the battlefield and not actively participating in the fight. This betrayal significantly reduced the strength and morale of the Nawab's army.

Consequences:
The British East India Company, with the help of Mir Jafar, emerged victorious in the Battle of Plassey. Siraj-ud-Daulah was defeated and subsequently captured and executed. Mir Jafar was rewarded by the British for his treachery and installed as the new Nawab of Bengal.

Significance:
The Battle of Plassey marked a turning point in Indian history as it established British control over large parts of Bengal. It paved the way for the British East India Company to expand its influence and eventually establish British colonial rule in India.

In conclusion, Mir Jafar's betrayal and collaboration with the British were instrumental in the British East India Company's victory at the Battle of Plassey. His actions not only led to the downfall of Siraj-ud-Daulah but also allowed the British to gain a stronghold in Bengal.

Option (C) is the correct answer