YAHWEH and God, are they the same being?

The word "God" is a title, but not a proper name. The title God is a generic English name used for the deity it is the generic word for a god (any deity). Hellenism was the cultural and philosophical perspective which spread from Greece through most of the ancient world from the year 333 BCE (the time of Alexander the Great) through 63 BCE (when Rome came to dominate). Because of this, many important elements of Greek culture - names, language, architecture, art, philosophy, etc. - influenced politics and culture throughout the Mediterranean region. Even Rome continued to spread aspects of Hellenism because Rome itself was so heavily influenced by Greece.