Klaus is consultative and full of sage advice, sometimes even wearing glasses and taking on a scholarly appearance. Klaus was once an East GermanOlympicski-jumper until his mind was transferred into the body of a goldfish during the 1986 Winter Olympics by the CIA to prevent him from winning the gold medal, leaving him permanently trapped in the goldfish's body. Klaus still hasn't come to terms with what happened, at times malcontent and gloomy. Not confined to his fishbowl, Klaus is often seen uniquely scooting himself about the Smith residence, reclined in a glass of water. In these moments, it's only his very lower back that's actually in the water. In the early going, Klaus had an obsessive crush on Francine Smith and often made sexual advances at her.For much of the series discounting its beginnings, the Smith family and particularly Roger have been shown to treat Klaus with disdain, take him for granted, and even mistreat him. Ironically, Klaus started out on the series as a bully, known for his ridicule and cruel teasing of all the show's main characters, particularly Roger.
Klaus and Roger's relationship is best described as a sibling rivalry. At times they hate each other and at other times they get along well. Roger is seen to be incredibly spiteful toward Klaus, saying things like "You can't participate Klaus, I hate you. I say that not out of anger but as a fact" in "Great Space Roaster" and "It's like you want to be kicked out of this family" in "The One That Got Away". Klaus does things to get Roger into trouble for his amusement, like when he tricked him in to eating Francine's potato salad in "Deacon Stan, Jesus Man". When a horrified Roger asked why Klaus would do something like that he just laughed and said "I'm German, it's what we do." In "A Piñata Named Desire", after Klaus made a comment about acting, Roger simply picked up Klaus's fish bowl, threw it across the room, smashed it against the wall, and walked out of the room as if nothing had happened while the fish lay gasping on the floor.
Although Roger has claimed to hate Klaus in the past, they do have a bond and are capable of being civil to each other such as when the head to Europe together in "Red October Sky". Further evidence of this can be seen in "Pulling Double Booty", as Roger and Klaus are quite content to watch a movie together and show annoyance when they must pause it as Stan intrudes with the cookie dough. Another example is that Klaus is often shown in the attic with Roger as he tends his fake bar in many disguises while in "Live and Let Fry" Roger dresses up as Klaus, the human, to help him get access to a family members will. In the end it turns out to be a trap to lure Klaus out of hiding and Roger gets beaten up due to the fact that Klaus owned some money to the East German Mafia. However, Klaus stays with him and keeps him company during his recovery, making sure Roger has sufficient pain medication to help him through it. Klaus was also the only member of the Smith family to remember Roger's birthday in "1600 Candles" and the alien seemed genuinely touched that he had bothered to prepare a birthday surprise for him.
The character was originally going to have a French accent. When Dee Bradley Baker came to audition for the character he ended up doing a German accent instead. Shortly after he was done with his audition the producers ended up casting him for the role.