Cow and chicken.

Cow and Chicken is an American animated series, created by David Feiss. The series shows the surreal adventures of a cow, named Cow, and her chicken brother, named Chicken. They are often antagonized by "The Red Guy", who poses as various characters to scam or hurt them. 

Cow, is Chicken's 7 year old sister, with a weight stated as 600 pounds. Cow looks up to Chicken, who she refers to as "Big Brother". She is often viewed by Chicken as infantile and stupid, and is quickly prone to emotional outbursts. She is the only character to appear in every episode of the show. Cow has employed Blackmail to get Chicken to do what she wants and often attempts to get the other characters to do the right thing. Cow's alter ego is "Supercow", a superhero with the ability to fly. 

Chicken, is Cow's 11 year old brother. He can be mean to his younger sister, and even to the rest of the family. He has a powerful ego, but in spite of this, has a powerful conscience, usually only displayed when Cow is in danger. His speech is riddled with malapropisms and sarcasm. Despite being a male, he demonstrated the ability to lay eggs. Chicken is very fond of ice skating. Like other chickens, he cannot fly, and is afraid of flying. Chicken is the only character in the show who knows that his sister and Supercow are the same person. 

source: http://en.wikipedia.org/wiki/Cow_and_Chicken

http://www.youtube.com/watch?v=6zXIScJ1LT8

Cow and Chicken are two characters that represent very well each one of our concepts. Cow is the personification of Robust, both physically and in personality. Chicken, instead, is the personification for Fragile.