What scientist invented calculus?
The calculus of single-variable functions was developed around the same time by two different mathematicians; Gottfried Wilhelm Leibniz and Sir Isaac Newton.
Newton was a very independent and solitary man, and he rarely published any of his works, save for a few select manuscripts which he shared with only a handful of colleagues. In fact; the actual process for his "method of fluxions" as it was known at the time was not actually published until 1736, nine years after his death. Leibniz on the other hand contributed heavily to the academic world through the Berlin Academy and so his calculus caught on more quickly throughout Europe.
At the time, the question of who truly invented calculus was a matter of very heated debate and controversy, perhaps with some nationalistic undertones. Leibniz was often accused of plagiarizing works from Newton, and vice versa. Today most historians agree that both men deserve equal credit for independently advancing the same field.