An intense guy who only smiled once, according to Newton's nephew.
He smiled once was when somebody mentioned they didn't rate Euclid much.
A little context - pretty much every proof back then was drawn out geometrically. Also, the ancients were thought to have occult wisdom far beyond what existed in 17th century Europe. The Roman army had retreated a millennium before and the continent still felt the loss. Losing valuable infrastructure such as aqueducts and roads would be like losing the internet and electricity today - civilisation has rolled back.
Rediscovering ancient knowledge meant amongst other things, finding the philosopher's stone, which in turn would get you executed - the King of England's gold reserves would be wiped if you could grow gold from lesser metals.
Physics was a 17th century hobby.
A bunch of people had made accurate measurements of various heavenly body movements, which were summed up by Kepler's three laws of motion and describe the rules by which the solar system's planets move.
The first rule to keep in mind, is that when nothing interferes with an object it should keep travelling. This is called inertia.
But the data collected by astronomers, showed that the planets move in an elliptical motion. As they go forward they drop a little.
By comparing how much the moon 'drops' over time as it travels around the sun; to how fast objects drop on the earth's surface; Newton showed that the distance dropped was the square inverse to the distance away from the centre of the earth.
Using the same data as Kepler; he brought solar system dynamics back down to earth.
Everything is falling.
We went from 'Keplerian' mathematical descriptions of our solar system to understanding how everything moves in the universe. An enormous shift.
Strangely, more than his studies into the occult, this new law of his, freaked Newton the-hell-out.
That one body may act upon another at a distance through a vacuum without the mediation of anything else, by and through which their action and force may be conveyed from one another, is to me so great an absurdity that, I believe, no man who has in philosophic matters a competent faculty of thinking could ever fall into it.
He was suspicious of gravity itself! And why not - you couldn't explain it.
How does gravity work? How do objects do the gravitational math and 'know' how to move?
Are there some sort of invisible 'gravity' molecules (aether) in between bodies which bump off each other causing a chain reaction?
How about a long distance wave which pulsed between objects?
The mechanism was only explained when Einstein came a long with a theory which poked a few holes into Newton's. Objects bend space-time, and it turns out that coupled with inertia the motion of planets are just the simplest most efficient paths for objects to take.
Never a fan of anecdotes, but that's all we have in finance, right?
Months after I came up with 'Sharpe Trajectories', I am still fond of them, which is uncharacteristic. Thinking about and visualising efficient paths makes so much sense.