Thaddeus is the nephew of Mrs. Weaver, next-door neighbor of the Flynn-Fletchers. Thaddeus, Thor and Mandy were visting their aunt for the weekend. He bears a strong physical resemblance to Phineas, but with curly brown hair and glasses, although his clothing style resembles Ferb's in that he wears high pants.
Thaddeus is arrogant and confident of his and Thor's building skills, challenging Phineas and Ferb to see who can build the biggest backyard fort. ("Thaddeus and Thor")
He and his brother Thor make an appearance in this fanfic.
In this episode, Thaddeus gains the ability to control electricity and transform his body into pure energy, but is defeated and is taken to the Tri-State Area Juvenile Detention Asylum for the Criminally Insane. In the alternate version, he isn't defeated, has his physical body destroyed, becomes a 5,000 foot tall energy bemoth, and dies at the end.
Thaddeus becomes Dupli-Man, an evil counterpart to Phineas' Multi-Man.
He makes an appearance with his siblings in this anime version of the show and his future wife is Patricia Verlean .
Like much of Stanville Thaddeus is getting along well with most of his team he is acting rather nice. He is in the Final 10. He was eliminated for saying that Lisa's hat was more of a bag.
Thaddeus hasn't appeared yet in Peanutjon's episodes, but is planned for the upcoming episode "Lady and the Trampoline" where he, along with Thor, appear at Louise's birthday party.
Thaddeus is married to Jessebel, and owns a business rivaling Phineas', he lives in a mansion across the street to the Flynn Mansion. Thaddeus has three children, two twins, Alex and Alexis, and the youngest, James.
Thaddeus grows up to be an Internet hacker/stalker/pervert, imitating to be a young, handsome boy. Thaddeus is later put in jail for life for certain things.