A mathematician is someone who uses mathematics in their work, typically solving problems related to a branch of mathematics including the sciences.
Leonardo Fibonacci introduced the modern decimal numeral system (the Hindu–Arabic numeral system) to Europe in 1202. Before this Roman numerals were used.
Blaise Pascal and Pierre de Fermat invented probability theory in 1654 to solve a gambling problem related to expected outcomes.
Isaac Newton produced many well-known works in math, astronomy, and physics, but he produced about as many unpublished works which dealt with theology, alchemy, and the occult.
Alan Turing can be considered “the father of computer science and AI.” Turing made major contributions to computing, codebreaking, and even helped the Allies win WWII.