Sentence:  Lucretius was the <WSD>Xenophanes</WSD> of Roman culture, a great theorist (visionary), an ardent disciple of Universal Nature, an enemy of all superstition, false gods, and false fear of death, ... 
Meaning of the word marked with <WSD> tags:  The pre-Socratic philosopher Xenophanes of Colophon; by extension or reference, any profound or transformative religious thinker.