The History of Calculus
The central themes of calculus are limits, functions, derivatives, integrals, and infinite series. the concept of calculus was created by Isaac Newton and Gottfried Lebniz who both claimed to have independently discovered calculus and accused the other of stealing his work and findings. Before Newton and Leibniz founded the concept, the word "calculus" was a general term used to refer to any body of mathematics. Newton came upon calculus in his investigations in physics and geometry, viewing the concept as the scientific description of the generation of motion and magnitudes. On the the other hand, Leibniz focused on tangency and came to believe that calculus was a metaphysical explanation of change. The two of them used their insight of past advances at understanding the mathematical concept to derive the idea that there was an inverse relationship between the integral and the differential of a function. If it wasn't for the combination of their knowledge and their desire to rise above the other, calculus would not be the complex concept we are studying in high school today. Most of Newton's findings came during the years of the bubonic plague (1665-1666) when he isolated himself and essentially discovered or created the Fundamental Theorem of Calculus, describing the period as “the prime of my age for invention and minded mathematics and [natural] philosophy more than at any time since.”
References: https://www.math.uh.edu/~tomforde/calchistory.html, http://www-groups.dcs.st-and.ac.uk/history/HistTopics/The_rise_of_calculus.html