When Britain relinquished rule of the Indian subcontinent in 1947, the area was divided into West and East Pakistan and India. What is today Bangladesh was under control of West Pakistan (today Pakistan) with a capital 1000s of miles away and across the Indian border.
Sheikh Mujib led the Bengalis of East Pakistan in resistance against the Pakistanis, whose military led a nine month genocide against them. India intervened on behalf of the Bengalis, and Bangladesh was created soon after.
However, two years after Sheikh Mujib was elected Prime Minister in Bangladesh’s first elections, he was assassinated along with his family in a coup. You can read about Sheikh Mujib and his rise and fall at the link.