Its pretty simple why Gandhi is on the note and someone like, say Raje Shivaji isn't. Shivaji was a staunch pro-Maharashtrian king who was well known for his rebellions against the Mughal (read: Muslim) masters. Such an act would alienate Muslim populations (which is exactly why Hindutva parties like Shiv Sena use him as his mascot). Prithviraj Chauhan would be a tip of the hat to the Rajput monachies of yore which the newly formed Indian republic did not want to acknowledge (especially right when they were stealing their kingdoms to form federalist states). Porus got his ass beat by that manlover Sikander.
Gandhi is completely safe because he openly preached love for all the ethnicities of India, but his actual politics definitely showed that he was not open minded to truly Revolutionary ideas (of Bhagat Singh, Bose, etc.) Still, when creating nationalist symbols for integration purposes, the Indian govt did not look for historical accuracy. They looked for political correctedness (intl recognition/martyrdom didn't hurt either). The safer the political symbol, the more easily it will be digested by the wide ethnic and religious gentry. For more on such revisionist histories, look at the Mexican Revolution and how its "heroes" have become national symbols when in reality Villa, Madero, Zapata, etc all equally hated each other and had their own motives.
The true freedom fighter that won India its independence was WWII. Thank god that shit destroyed Europe's economy or else colonial powers like Britain and France would never relinquish their empires
