It's a bit tricky to pinpoint a single date for the "creation" of the formula for relativity, as it developed over time. Here's a breakdown:

* Special Relativity: The foundational work was published by Albert Einstein in 1905 in his paper "On the Electrodynamics of Moving Bodies." This paper included the famous equation E=mc², which relates energy (E) to mass (m) and the speed of light (c).

* General Relativity: Einstein developed his theory of general relativity over several years, finally publishing his work in 1915. This theory extended special relativity to include gravity, but it doesn't have a single "formula" like E=mc². Instead, it involves a set of equations describing the curvature of spacetime.

So, while we can say that E=mc² was "created" in 1905, the development of relativity as a whole was a more gradual process.