Complex sentence: ML Pin became the first director of the school, which was the country's first coeducational, and is now known as Triam Udom Suksa School and widely regarded as one of the best schools in the country.
Split into simpler sentences: ML Pin became the first director of the school, the country's first coeducational school, now known as Triam Udom Suksa School. It is widely regarded as one of the best schools in the country.