Rajkumar was the first person in Kannada cinema to get President's Silver medal in 1963, best actor award was instituted only in 1967. Vasudev Rao and Charu Hassan then won the best actor awards.
I Think the First Kannada Actor to get teh National Award was Sri Vasudev for his role as Choma in the film Chomana Duddi in the lates 70s or early 80s.