The successor to Albert Einstein's theory of special relativity was Albert Einstein himself. After developing the theory of special relativity in 1905, Einstein continued his research and eventually formulated the theory of general relativity, which he published in 1915.
It's important to note that the theory of special relativity was not superseded or replaced by general relativity. Rather, general relativity is an extension of special relativity that incorporates the effects of gravity. Special relativity deals with objects moving at constant speeds in the absence of gravity, while general relativity includes the gravitational force and describes the curvature of spacetime caused by massive objects.
Albert Einstein chose to pursue the theory of general relativity because he was unsatisfied with the limitations of special relativity, which did not incorporate gravity. He wanted to develop a more comprehensive theory that would provide a unified description of space, time, and gravity. Einstein's motivation to work on general relativity was driven by his belief that gravity was not simply a force acting at a distance, but rather a curvature of spacetime caused by mass and energy.
The development of general relativity was a challenging task that required complex mathematical equations and rigorous calculations. It took Einstein nearly ten years to refine the theory and address various technical issues. Despite the difficulties, Einstein persisted in his research and eventually succeeded in formulating the theory, which has since been confirmed by numerous experiments and observations.