Aurangzeb came to power after winning the war of succession and by defeating his three brothers

Aurangzeb, the sixth Mughal emperor, came to power after a war of succession against his three brothers. He defeated his older brother Dara Shikoh, who was considered the rightful heir by their father, Shah Jahan. The war among the Mughal princes is known as the War of Succession or the War of the Four Princes. Aurangzeb emerged victorious and subsequently became the Mughal emperor.

Shuja (Option B), Askari (Option C), and Murad (Option D) were other brothers of Aurangzeb who were also contenders in the succession struggle. However, it was his victory over Dara Shikoh that played a significant role in Aurangzeb's ascension to the throne.

Therefore, the correct option is Option A: Dara, as Aurangzeb came to power after defeating his older brother Dara Shikoh in the war of succession.