Thaddeus and Thor are a pair of characters who appear as antagonists in the Phineas and Ferbepisode of the same name. They are the nephews of Mrs. Weaver, the Flynn-Fletchers's next-door neighbors. Thaddeus 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. Thor bears an uncanny resemblance to Ferb, except that he is bulkier and has yellowish-brown hair.
While nowhere near the level of Phineas and Ferb, Thaddeus and Thor show an above average skill in building and design, considering that their fort is beyond what most other normal children could create, especially in such a small amount of time.
Thaddeus is arrogant and confident of his and Thor's building skills, challenging Phineas and Ferb to see who can build the best backyard fort. Thaddeus is the only one of the duo who speaks.
Not much is revealed about Thor's personality, as he is extremely laconic (like Ferb). Unlike Phineas, who treats his brother as an equal and a partner in his projects, the arrogant Thaddeus treats Thor like his sidekick/lackey. When Thaddeus snaps his fingers and orders "Gum me!", Thor hands him a piece of bubblegum.
Role in the episode
In the episode they appear in, Thaddeus, Thor and their older sister Mandy visit their aunt for the weekend. Both Mandy and Candace argue over whose brothers are more annoying and competent. Phineas and Ferb, at Candace's request, agree to compete with Thaddeus and Thor to see who can build the best backyard fort. Thaddeus and Thor build a castle-like fort complete with a slide and a licorice dispenser, which becomes insignificant when compared to Phineas and Ferb's 20-story fort with a swimming pool and a bowling alley.
Thaddeus and Thor went oddly unmentioned in Mandy's next appearance, "Perry the Actorpus". However, they, along with Mandy, later made a brief, silent reappearance as contestants at the fish show in "Great Balls of Water".
They are the archenemies of Phineas and Ferb despite not being the main antagonist of the show