By 1939, Gandhiji had become such a towering personality that nobody was ready to contest against the candidate that was put by Gandhiji for the post of President of INC. Whosoever Gandhiji suggested to be the President of the Congress, he was to be selected. And Gandhiji in the Tripura session selected a man called Pattabhi Sitaramayya.
But Subhas Chandra Bose objected to his selection and said "I would like to become the President of the Congress". It wasn't because he was after power. But he wanted to give a proper direction to the organisation. According to him, Pattabhi wasn't the right man. But Gandhiji stated NO, and said that "whatever name I have suggested is final." Something like the modern High Command culture of the Congress. Believe it or not, it was Subhash Chandra Bose who openly challanged Gandhiji stating that now I'll contest the elections.
Now, it was for the first time, Gandhiji took a Political initiative in campaigning in favour of Mr. Pattabhi Sitaramayya and he went on to the extent to make a statement that "If Pattabhi Sitaramayya is defeated, it is my defeat". And, Pattabhi Sitaramayya was defeated. And S.C. Bose was elected with thumping majority as the President of the Indian National Congress in the Tripura Session.
And when he was elected, Gandhi went to S.C. Bose to congratulate him and while delivering the congratulatory speech. Gandhiji addressed him as "Netaji". Meaning, that you have now become the leader of the leaders. And from then onwards, he came to be known as the Netaji Subhas Chandra Bose.
To which, our Netaji replied and conferred the Title of Rastrapita or the Father of the Nation to Gandhiji.