V. Nagam Aiya

Dewan Bahadur/Diwan Bahadur was a title of honor awarded during British Raj. It was awarded to individuals who had performed great service to the nation. It was an equivalent of the "Civil Division" of the British Order of the Bath. The title was accompanied by a medal called a Title Badge. Dewan literally means Prime Minister in Indian context and Bahadur means brave.
This title was above Rao Bahadur title and usually people with Rao Bahadur were elevated to status of Dewan Bahadur.
Further, the Prime Ministers of Indian Princely States were known as Dewan/Diwan. They were also given or promoted directly to the title of Dewan Bahadur by British authorities on being appointed as Dewan, to suit their post. Provided by Wikipedia
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