Complex sentence: He left the "tol" in his late teens (c1465) to attend to his responsibilities as the Shiromani Bhuyan, and came to be known as the "Dekagiri".
Split into simpler sentences: He left the "tol" in his late teens (c1465) to attend to his responsibilities as the Shiromani Bhuyan. He came to be known as the "Dekagiri".