Jacob Trevor Flynn is Phineas and Isabella Flynn's son. He is the oldest out of three children. His siblings are Angela and Julia "Marie"Flynn.
Jacob is a triangle headed boy, short for his age, and he has a higher pitched voice. Instead of red hair like Phineas's, he has raven black like Isabella's. He sometimes uses her catchphrase; "Whatcha' Doin?". He helps his sisters Angela and Julia, along with his cousins, David, Lizzie, and Thomas Fletcher bulid summer inventions. He usually is seen hanging out with David Fletcher and Jasmine Rai. (Who currently has a small crush on him.)