Answer:
Even before Sir Isaac Newton was born, roughly 16 out of every 19 people had already noticed that when they jumped out of bed, their feet went to the floor, and that when they dropped something, it fell to the ground. Gravity was already quite universally known, whether or not that's what anybody called it, and it didn't need to be discovered.
All Newton did was to accurately describe how it works.
Furthermore, he took the INCREDIBLE leap of stating that the gravity we experience on our Earth also influenced the motions of planets around our Sun.