A great French philosopher and mathematician. One of Descartes's theories attempted to explain the workings of the solar system by suggesting that space was filled with infinite, miniscule, invisible particles, whose motion created vortices that whirled the planets around the sun. The theory enjoyed popularity in the 17th century but was eventually displaced by Newton's theory of universal gravitation.
An astronomer in the Royal Society, and the namesake of Halley's Comet. Halley was a close friend of Newton, and assisted in the publication of the Principia.
A prominent scientist in the Royal Society, of which he was first secretary, and then president. Hooke became a rival of Newton in the 1670s, when the two men quarreled over their respective theories of light. He later felt that Newton had stolen from him the idea for the mathematics of gravity, and when Newton won fame after the publication of the Principia, Hooke grew bitter and deeply resentful.
Gottfried von Leibniz
A brilliant German mathematician, and a contemporary of Newton. The two men developed a bitter feud in the early 1700s over who had first invented calculus.
Newton's mother. His father died before he was born, and when Isaac was only three Hannah remarried and moved away, leaving the boy to be raised by an uncle. This abandonment must have been traumatic for the young Isaac; many biographers have speculated about its impact on his later psychological make-up-- specifically his fierce insecurity.