Complex sentence: A much less controversial figure than John Calvin or Martin Luther, his importance has long been underestimated; recent research shows that he was one of the most influential theologians of the Protestant Reformation in the 16th century.
Split into simpler sentences: A much less controversial figure than John Calvin or Martin Luther, his importance has long been underestimated. Recent research showed, though, that he was one of the most influential theologians of the Protestant Reformation in the 16th century.