Dylan Flannigan is the son of Brian Griffin and Tracy Flannigan, introduced in "The Former Life of Brian". Brian left Tracy before Dylan was born, leaving him not knowing what it's like to have a father. When he visits Tracy, she had become a fat slob. Tracy told Brian and Stewie about Dylan when they went to visit her. Brian goes back to the house and tells Peter and Lois about him. Tracy soon drops Dylan off at Brian's so father and son could bond. At first, he was disrespectful towards Brian and his family. When he is introduced to Chris, the Evil Monkey comes out of the closet, only to have Dylan brutally beat him. When Brian decided he was finally going to give up, one of them dropped a bag of pot. They both called out for it. While smoking the pot they realized they had a lot in common and became close. Brian soon became very protective of Dylan.
Brian was very tired of Dylan's bad attitude, so he turned him into a nicer person. Peter, sick of Brian's overemotional reactions to the slightest things, convinced Tracy to take Dylan back. Even though Brian was against it, Dylan said he must go because he can change his mom's life the same way Brian changed his. Dylan hasn't been seen since.
Dylan is voiced by Seth Green.
Dylan's creation is questioned, due to the fact that he is age thirteen and Brian is only seven years old. Stewie asked this question, only to have Brian tell him to "Go on the Internet and complain." Also, Dylan appears to be fully human mostly from Tracy's genes, even though his father Brian is a dog, so Dylan is actually half-human, and half-dog.