Famous for Zeno's paradoxes . Empedocles of Acragas (c. 490 - 430 BCE). Believed in metaphysical doctrine of four elements. Advocate of ethical vegetarianism . Protagoras of Abdera (c. 481 - 420 BCE). Sophist . Early advocate of relativism . Hippias (middle of the 5th century BCE). Sophist . Gorgias .