Senta

is a loan shark from the Akagi family.

Background
He was sent with his brother, Bunzō to collect money that Tsunade owes to their boss. To blackmail her, they steal the First Hokage's Necklace.

Part I
They believed that it still belonged to Tsunade. However, it belongs to Naruto Uzumaki, who fights them to get the necklace back. Afterwards, they explain their position (either they get the money back, or they have to keep trying to get it back without getting to go home and see their families). Naruto then agrees to collect on Tsunade's debt. Ironically, at the end of the episode Tsunade shares with everyone that she paid the brothers' boss back his money when she and Shizune had visited their village ten years before.