Step 1: Understand the question.
We are given a real birth name, Gummadi Vittal Rao, and asked which famous person this is.
Step 2: Why a pen name.
Many singers and activists take a new name that shows their cause. They often drop their birth name in public life.
Step 3: Who this person is.
Gummadi Vittal Rao was a well known poet, singer, and revolutionary from Telangana.
Step 4: The famous name.
He became famous as Gaddar. He picked this name in honour of the Gadar Party, which fought for India's freedom long ago.
Step 5: His work.
He used songs and writing to speak for poor people and to ask for social justice in Telangana.
Step 6: Conclusion.
So Gummadi Vittal Rao is the singer known as Gaddar.
Answer: Gaddar