French mathematician Évariste Galois was a B-list genius whose work made otherwise insoluble equations possible to calculate with and solve, and also made it easier to determine when an equation could not be solved analytically. His methods are used today in solving difficult questions in particle physics, among other things.
But, due to his untimely death in a duel at the age of twenty, the point at which his work was widely known and appreciated was delayed more than seventy years.
We will never know what other great discoveries this prodigy might have made had he lived a full life. There is every reason to think that some scientific discoveries might have been made a generation or two earlier if he had lived. Even science today might have reached greater heights with access to mathematical tools that have not yet been devised that he might have invented.
In 1830 [Évariste] Galois (at the age of 18) submitted to the Paris Academy of Sciences a memoir on his theory of solvability by radicals; Galois' paper was ultimately rejected in 1831 as being too sketchy and for giving a condition in terms of the roots of the equation instead of its coefficients. Galois then died in a duel in 1832, and his paper, "Mémoire sur les conditions de résolubilité des équations par radicaux", remained unpublished until 1846 when it was published by Joseph Liouville accompanied by some of his own explanations. Prior to this publication, Liouville announced Galois' result to the Academy in a speech he gave on 4 July 1843.