Sergei is a man obsessed with communism and getting revenge on Stan in "Red October Sky" after Sergei's son grew up to sell Halloween costumes to dogs as his job. He plans to do this by eventually making a "Stew seasoned with revenge". Despite this, they do seem to get along, such as when Sergei dropped off Stan's mail that was accidentally dropped off in his mailbox where only moments before he threatened to get his revenge. In "Phantom of the Telethon", Sergei trains Boris the Russian Circus Bear. Sergei is voiced by Steve Hely.