We have to identify the adjective clause first. The two clauses in the sentence are: (a) Albert Einstein is a great inspiration to me (main clause) (b) whose theories changed science forever (subordinate clause) Since it follows that adjective clauses are always the subordinate clause, then "whose theories changed science forever" is the adjective clause that modifies Albert Einstein. It contains the relative pronoun whose. Now, whose is a possessive determiner. It implies the theories are owned by Albert Einstein.
What is the function of the relative pronoun in the adjective clause? Albert Einstein, whose theories changed science forever, is a great inspiration to me.