Klaus and Claudia Vorstein are the antagonists of the cartoon movie The Chipmunk Adventure - which featured the famous Alvin and the Chipmunks as well as the Chipettes.
Klaus and Claudia Vorstein tricked the Chipmunks into aiding them in smuggling diamonds across the world under the guise of a ho 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.
The 2 criminals 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 she 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.
Luckily the Chipmunks manage to delay the two criminals long enough that Dave arrives in time to hear Alvin calling for help, with Dave's arrival both Klaus and Claudia try to escape but are ultimately captured and arrested.