Klaus Furschtein is the secondary antagonist, the main being Claudia Furschtein, of the 1987 cartoon movie The Chipmunk Adventure.
He is voiced by Anthony DeLongis.
He and Claudia tricked the Chipmunks into aiding them in smuggling diamonds across the world under the guise of a hot air-balloon race across the world, taking advantage of an argument between Alvin and Brittany after playing an arcade game based on the novel Around the World In Thirty Days.
Klaus and Claudia give each team (Chipmunks and Chipettes, respectively) small dolls in their image that they are to place at each location they arrive at as prove of their travels - the first team to win the race will be rewarded with a cash prize.
What the Chipmunks are unaware of is each of these dolls is actually stuffed with diamonds, thus they agree to the terms - unaware that they are aiding the smugglers.
However during their travels the Chipettes become distracted when they discover a baby penguin and try to take it back to its family, Claudia (unaware of this) believes the girls had found the hidden diamonds and were trying to make an escape with them - thus when they diverted from their usual course Claudia had her henchmen go forth to capture the girls and retrieve the diamonds.
Claudia's henchmen catch up with the Chipettes as they are delivering the baby penguin to its family, when the thugs try to take the dolls the girls fight back - ripping the dolls in the process and revealing the diamonds: luckily the penguins, grateful to the Chipettes for returning their baby, chase off the henchmen.
Now aware of what was happening the Chipettes head off and find the Chipmunks, together the two groups fly back to Los Angeles - however when they arrive at the airport, Klaus and Claudia are waiting for them and attempt to kidnap them.
The Chipmunks and Chipettes are forced into a 1935 Rolls-Royce Silver Cloud I under the false threat of Miss Miller being kidnapped. At the same time, Dave is arriving home to the airfield, and hears Alvin's cries for help. Inspector Jamal runs up, identifying himself, and he and Dave begin to make chase in his 1987 Chevrolet Caprice but two other cars crash into each other and block them off at an intersection. While it at first appears that Klaus and Claudia will escape on a private jet to Costa Rica, they are accidentally run off the road by none other than Miss Miller, who was heading to the airfield to pick up Dave. Klaus and Claudia are then taken away by the police.