Step 1: Understanding the Concept:
Brahmi is the mother of most modern Indian scripts. Its meaning had been lost for nearly a thousand years until the $19^{th}$ century.
Step 2: Detailed Explanation:
James Prinsep was an officer at the Calcutta Mint and a leading figure in the Asiatic Society of Bengal.
He spent years studying the inscriptions found on pillars and rocks across India, as well as on ancient coins.
By comparing bilingual Greek-Brahmi coins from the Indo-Greek kings, he managed to crack the code of the Brahmi script in 1838.
This discovery allowed historians to read the edicts of Emperor Ashoka, fundamentally changing our understanding of early Indian history.
Step 3: Final Answer:
James Prinsep is the individual who deciphered the script.