Answers (2)
Gravitational force (or gravity, if you will), the three laws of motion, he proved that the earth rotates around the sun, his laws underpinned man leaving the earth (and landing on the moon). He discovered the calculus, his work in optics led us to understand the nature of light, he invented the reflecting telescope, did work in thermodynamics.
On top of all that, the reason coins have ridges around the rim are because of his idea to prevent fraud. And he invented catflaps. :)
He was, I believe, the most important and influential scientist to ever live.
I'm a huge fan of Tesla too, especially the things he did which are still unrepeatable. He was a brilliant, brilliant scientist and a genuinely original thinker. I think he, rather than Einstein, should be known as the great mind of the early 20th century.
But I will defend Newton to the death. In terms of moving things forward, he was influential in disparate fields and he had that touch of genius (to make a connection where nobody previously had) that many scientists don't have. I'll give you Tesla as an exception to that. Tesla was a genius. But chemistry, optics, religion, gravitation, mathematics, astrophysics, philosophy, mechanics? That is a broad church indeed to make advances in.
Isaac Newton was a great scientist and inventor. But he wasn't the best. I personally am a big fan of Leonardo Da Vinci, Nicola Tesla, and also Ctesibius.