Rashtrapita

"Rashtrapita" or "Rashtra pita" translates to "Father of the Nation".  Somewhere along his career, Mahatma Gandhi acquired that appellation.

Per a 2012 article in the Hindustan Times, a ten-year old girl, under RTI (Right to Information) asked the government when Gandhi acquired "Father of the Nation" status,  and the government archivists were flummoxed.

Who named Mahatma Gandhi 'father of nation'? Govt foxed
April 4, 2012

A Lucknow girl's simple query to know if Mahatma Gandhi was ever conferred the title of 'The Father of The Nation' has come a cropper.

From the Prime Minister's Office (PMO) to the ministry of home affairs (MHA) no one seems to really know the answer to the 10-year-old's question.

They coolly forwarded the RTI plea of class VI student Aishwarya Parashar to the National Archives of India (NAI), the body that claims to be the repository of the non-current records of the Government of India. Surprisingly, the NAI, after a hectic search in their records, was unable to find the desired information and requested Aishwarya to come and search for it in NAI's public records and library material herself.

Jayaprabha Ravindran, assistant director of archives and chief public information officer (CPIO) wrote back in a letter dated March 26: "As per search among public records in the National Archives of India, there are no specific documents on the information sought by you."

The maintainers of Gandhiana credit Subhas Chandra Bose:

...it was Netaji Subhash Chandra Bose who first addressed him as such in his condolence message to the Mahatma on the demise of Kasturba.

Ba and Bapu had been interned at Aga Khan Palace, Pune in the wake of the Quit India Movement. It was while serving the prison term Kasturba passed away on 22 February, 1944.

Concerned about Gandhiji, Netaji sent the following message to the Mahatma on Azad Hind Radio, Rangoon on 4th June, 1944.

"...........Nobody would be more happy than ourselves if by any chance our countrymen at home should succeed in liberating themselves through their own efforts or by any chance, the British Government accepts your `Quit India' resolution and gives effect to it. We are, however proceeding on the assumption that neither of the above is possible and that a struggle is inevitable.

Father of our Nation in this holy war for India's liberation, we ask for your blessings and good wishes".

Note that this is after the death of Kasturba Gandhi.  But Women in the Indian National Movement: Unseen Faces and Unheard Voices, 1930-42, by Suruchi Thapar-Bjorkert (2006), mentions an article in the Hindi magazine Saraswati: Devidutt Shukla, Rashtra Mata Kasturba, Saraswati, September 1938.  "Rashtra Mata" translates to "Mother of the Nation".

This suggests that Mahatma Gandhi got this appellation earlier than 1944.

Note also that people called Gandhi "Bapu" or "Bapuji" - "father" - an honorific for an elderly man; and it might be an easy observation someone made that a nation calls him "father".