Complex sentence: Of those, Rastko Nemanjić became the most notable historic figure of all Serbian history, known as Saint Sava who was the first Serbian Archbishop and is regarded as the founder of Serbian law and literature.
Split into simpler sentences: Of those, Rastko Nemanjić became the most notable historic figure of all Serbian history, known as Saint Sava. He was the first Serbian Archbishop, and is considered the founder of Serbian law and literature.