Complex sentence: Amar Nath Kak (1889--1963) was a prominent Kashmiri lawyer and author who's most important books are "Hamara Vrittanta" and the "Gayatri", both written in Hindi.
Split into simpler sentences: Amar Nath Kak (1889--1963) was a prominent Kashmiri lawyer and author. His most important books are "Hamara Vrittanta" and the "Gayatri", both written in Hindi.