Who introduced the concept of Pure theory of Law?

The idea of a Pure Theory of Law was propounded by the formidable Austrian jurist and philosopher Hans Kelsen (1881–1973). Kelsen began his long career as a legal theorist at the beginning of the 20th century.  Kelson’s theory suggests that there is no need of explanation of natural law when it includes elements of politics, sociology or other elements. He believed that to understand the pure or natural law any possibility of morality or sociology or any other element should be excluded. So that’s why the theory is ‘pure’ and called Pure Theory of Law.