Lupin the 3rd

Fujiko and a mystery man come bringing a request that Lupin steal a mountain of gold bullion from a Swiss bank, which is renowned throughout the world for the strength of its security. The man's idea, for them to join forces, steal the gold from underneath the vault, melt it down, and remold it so as to look like the body of a truck, is carried out to that point. What is the man's true identity? Who will have the last betrayal?