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")