|Family|| Gordon Сlaw (grandfather)|
|Location||Some sort of boarding school|
|Portrayed By||Alex Doduk|
William "Billy" Thaw is Dr. Claw's nephew, Talon's cousin and one of Penny's romantic interests. He only appeared in "Claw's Nephew."
He was sent by his grandmother to stay with his uncle, Dr. Claw to become evil just like all of his relatives while he is on spring break from boarding school. He meets Penny, who is on a mission with Inspector Gadget and the Gadgetinis. Penny quickly develops a crush on him and he takes her and the rest of the Gadgets to his uncle's house for dinner.
When William found out his uncle was evil, he called his grandma to warn her. Of course, his grandma was evil too and didn't understand at all. This caused Claw to blow up his lair and for William and the others to escape safely. However, Claw and MAD Cat escaped as well in Claw's plane. It is never revealed what happened to William at the end, but he probably went back to boarding school or with his grandmother.
He is a handsome young boy with large square glasses, blue eyes. and brown hair. He also wears a shirt with a vest, and in that shirt, has tie.
William is not evil or cruel like his father and uncle. He is quite a knowledgeable boy who only ever wants to help people, much to the dismay of his entire family. He also has an innocent crush on Penny, just as she has a crush on him. He also was blissfully unaware of Claw or his family's "evilness", yet he seemed to care about his family all the same.
- In the 2015 series, Claw has another nephew named Talon, who is also William's cousin. Penny also has a crush on Talon who in turn has a crush on her. However Talon is evil and desires to be a villain like the rest of their family and works for his uncle as a MAD operative resulting in him and Penny developing a rivalry like their uncles despite the mutual attraction between them as Penny is an HQ agent-in-training.