Explanation:

Three Presidency banks were set up under charters from the British East India Company- Bank of Calcutta, Bank of Bombay and the Bank of Madras. These three banks were: i) Bank of Bengal (Bank of Calcutta)-1806; ii) Bank of Bombay-1840; iii) Bank of madras-1843.  In 1921, these Presidency banks were merged and formed Imperial Bank of India. Imperial bank of India was renamed as State Bank of India in 1955, So we can trace the orgin of SBI from Bank of Bengal.