Final answer:
Rene Descartes is regarded as the father of modern philosophy, famously formulating the statement 'I think; therefore I am' as a starting point for existence.
Step-by-step explanation:
The individual regarded as the father of modern philosophy for defining a starting point for existence with the statement 'I think; therefore I am' is Rene Descartes. This statement, known as Cogito, ergo sum in Latin, serves as a fundamental element in Western philosophy, establishing the basis for modern thought and subjective rationalism. Descartes' philosophy challenged the traditional teachings at the time, which were primarily based on Aristotelian and Scholastic principles. He sought to build a foundation for knowledge based on reason and doubt, differentiating his approach from that of previous philosophical thinkers such as Socrates, Plato, and Aristotle.