It was proposed by Arnold Sommerfield to try to cover the deficiencies that the Bohr model presented. Therefore, it is a relativistic version of the Rutherford-Bohr model and was based, in part, on Albert Einstein's relativistic postulates.
Bohr's atomic model was seamless when it came to the hydrogen atom. However, when it came to atoms of other chemical elements, the electrons of the same energy level had different energy.
Therefore, he asserted a number of corrections to the model:
He discovered that the electrons of certain atoms reached speeds close to that of light. He performed the calculations for relativistic electrons.