Final answer:
Panini was the Sanskrit grammarian who refined the written language of Sanskrit, and his work is one of the most comprehensive grammatical treatises in history.
Step-by-step explanation:
The Sanskrit grammarian who refined the written language of Sanskrit was Panini. Panini's work, especially his formulation of the 3,959 rules of Sanskrit morphology, syntax, and semantics in the grammer treatise called the Ashtadhyayi, is considered one of the most comprehensive and scientific works of grammar ever created. His impact on Sanskrit is comparable to that of subsequent luminaries in the Gupta period who contributed significantly to literature and sciences, such as the poet Kalidasa, the scientist Aryabhatta, and the mathematician Brahmagupta. During this era, famed texts like the Mahabharata, Ramayana, and treatises like the Upanishads were composed or compiled in Sanskrit, underscoring the language's cultural and scholarly significance.