In Hindu Varna system, politics, war and ruling the kingdom is Dharma of Kshatriya. Similarly, Dharma of Brahman is to learn, teach, perform Yadnya and other vedic activities, advice the king etc.
On the other hand, Sages are quit from normal life. They are not generally interested in things like ruling the kingdom.
Are there any examples of Brahman or Sage became King (ruled the kingdom) in Hinduism?
One example I remember is Parshuram; but I am not sure if that is correct.