Maybe Galois with group theory? He died in 1832, but his work was only published in 1846, upon which it kicked off the development of group theory, e.g. with Cayley’s 1854 paper defining a group. Claude writes that there was not much progress in the intervening years:
The period between Galois’ death in 1832 and the publication of his manuscripts in 1846 did see some developments in the theory of permutations and algebraic equations, which were important precursors to group theory. However, there wasn’t much direct progress on what we would now recognize as group theory.
Some notable developments in this period:
1. Cauchy’s work on permutations in the 1840s further developed the idea of permutation groups, which he had first explored in the 1820s. However, Cauchy did not develop the abstract group concept.
2. Plücker’s 1835 work on geometric transformations and his introduction of homogeneous coordinates laid some groundwork for the later application of group theory to geometry.
3. Eisenstein’s work on cyclotomy and cubic reciprocity in the 1840s involved ideas related to permutations and roots of unity, which would later be interpreted in terms of group theory.
4. Abel’s work on elliptic functions and the insolubility of the quintic equation, while published earlier, continued to be influential in this period and provided important context for Galois’ ideas.
However, none of these developments directly anticipated Galois’ fundamental insights about the structure of solutions to polynomial equations and the corresponding groups of permutations. The abstract concept of a group and the idea of studying groups in their own right, independent of their application to equations, did not really emerge until after Galois’ work became known.
So while the 1832-1846 period saw some important algebraic developments, it seems fair to say that Galois’ ideas on group theory were not significantly advanced or paralleled during this time. The relative lack of progress in these 14 years supports the view of Galois’ work as a singular and ahead-of-its-time discovery.
Maybe Galois with group theory? He died in 1832, but his work was only published in 1846, upon which it kicked off the development of group theory, e.g. with Cayley’s 1854 paper defining a group. Claude writes that there was not much progress in the intervening years: