Final answer:
Heraclitus of Ephesus is recognized in today's textbooks for his influential philosophy that all is in flux and his concept of Logos, signifying the ever-changing yet orderly nature of the universe.
Step-by-step explanation:
Heraclitus of Ephesus is mentioned in modern textbooks because he was a pre-Socratic Greek philosopher who made significant contributions to metaphysics and epistemology. His doctrine that reality is in a state of constant flux and that the universe is governed by a rational principle or Logos was groundbreaking. One of Heraclitus's most famous statements, "[It is not possible to step twice into the same river]... It scatters and again comes together, and approaches and recedes", encapsulates his belief that change is the only constant. Contrary to Parmenides, who believed in an unchangeable reality, Heraclitus saw the world as a domain of diversity and transformation. These philosophical contributions have influenced several areas of study, including ethics, politics, and science.