For most of "Evil Valentine's Day", Alex and Clover are smitten with Guillaume as they think he has a crush on one of them. However, after Jerry (who is fluent in French) translates what Guillaume (who can not speak English) is saying into English, they realize that he is not interested in any of the girls but just his work as a pool boy.
While Jerry and the girls are at Euro-WOOHP headquarters in Paris, France, they meet up with Guillaume again in "Evil Shoe Designer". For most of the episode, the girls think he has a crush on Samantha. But at the end, they again find out that Guillaume just wanted to take on Sam as his apprentice in his work as a pool boy as she was anatomatically perfect for it.
According to an interview with David Michel, Guillaume was created by Bob and Michelle and was named after a development executive of the same name.