Klaus Furschtein is one of the main antagonists that appear in 1987 film The Chipmunk Adventure along with his younger sister, Claudia Furschtein. He and Claudia's dog, Sophie, don't have a good relationship and constantly try to make the other look bad in front of Claudia.
Klaus and Claudia find themselves in a difficult position with their illegal diamond smuggling operation as they no longer have any couriers that can deliver their contraband to their buyers without being caught by police, led by INTERPOL Inspector Jamal. When they overhear The Chipmunks and The Chipettes arguing over who would win a real game of Around the World in 30 Days, mostly Alvin and Brittany, Claudia decides to use them as the Furschteins' couriers to deliver the diamonds under the surmise that the winners would receive a prize of $100,000. Though Klaus has his doubts and concerns on the matter, his younger sister overrules him as she wants to lead this operation and ensure their smuggling can continue despite Jamal's interference.
However, as time passes, Klaus and Claudia learn that the Chipettes have diverted from their assigned delivery route, unaware that they were returning a baby penguin to its family in Antarctica. Fearing the Chipettes have caught onto their scheme, Claudia dispatches her men to capture them and retrieve both the remaining diamonds and the collected money from the buyers.
Later, the Furschteins are waiting for the Chipmunks and Chipettes at the airport when the Chipettes' balloon crashes onto the tarmac. Acting like they are still glad to see both teams made it back safely, they soon learn that the Chipmunks and Chipettes have discovered the scheme and will have no part in it any longer. After a chase through the airport terminal, Klaus and Claudia manage to force the Chipmunks and Chipettes into their car under threat of kidnapping Miss Miller if they don't cooperate. Klaus is just forcing Alvin into the car when Alvin's hat is blown off by the wind, allowing Dave, who had just exited the terminal after returning from his trip to Europe, to find it and discover that the Furschteins have kidnapped the Chipmunks and Chipettes. Dave and Jamal give pursuit in a marked police cruiser loaned to Jamal by the local police, but the Furschteins are able to cause a traffic accident to lose them. As Klaus and Claudia believe that, in minutes, they will be on their way to Costa Rica and safety on their private jet with the Chipmunks and Chipettes as their hostages, karma catches up to them when Miss Miller, driving the wrong way up the highway to the airport to pick up Dave after missing her exit, causes their car to swerve to avoid her and crash into a lamppost, wrecking it and allowing Jamal to soon arrive with police backup to take the Furschteins into custody. Klaus can only sarcastically toast his sister on how they nearly had victory in their clutches before being handcuffed and placed in the back of a cruiser to be taken to prison.