Recently I saw the serial called Suryaputra Karn. There is a character called Paundraka Vasudeva who claims that he is the Original Vasudeva.
Who is this Paundraka Vasudeva?
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(I spell Krishna as Krsna.)
Paundraka Vasudeva was the King of Pundra (hence his name was Paundraka - 'The King of Pundra'). The capital city of Pundra was Karusha. (Also it is PauNDraka as in the Da in Damaru, not Paundraka like they say in the serial.)
Paundraka was the son of King Vriddhasharma and Queen Shrutadeva. Shrutadeva was the sister of Vasudeva, Krsna's father. Paundraka's brother was Dantavakra, who was the rebirth of Kumbhakarna (and indirectly Vijaya, the doorkeeper of Vishnu).
Paundraka's story is described in the 66th Chapter of the 10th Canto of Srimad Bhagavatam. The ministers of Paundraka once told him how great he was, comparable to Lord Vishnu. Due to this, he began thinking himself to be an avatara of Lord Vishnu. But since people already believed that Krsna was Vishnu's avatara, he decided to kill Krsna and prove that he was the real Vaasudeva. (here Vaasudeva means Vishnu, not son of Vasudeva.)
Therefore he sent a message to Krsna insulting him and ordering Krsna to give Paundraka his Sudarshana Chakra, Panchajanya Conch, Kaumodaki Gada and other weapons. Krsna laughed at Paundraka's foolishness and went with his army to Paundraka's kingdom.
After a fierce fight, Krsna threw his Sudarshana Chakra at Paundraka and killed him, as well as Paundraka's friend Kashi-raja. Later on, Kashiraja's son Sudakshina wanted to take revenge on Krsna. He performed a Tantrik Yajna and created a demoness to destroy Krsna. But Krsna once again sent his Sudarshana Chakra and since the demoness was afraid of the Chakra she returned to Kashi to kill Sudakshina. The Chakra followed her and after destroying Sudakshina and the demoness, it burnt the city of Kashi and returned to Dvaraka.
P.S. What they are showing in the serial, of Duryodhana taking Paundraka's help and Karna fighting Paundraka is complete nonsense. Nothing of that sort happened.