Franklin Fat-Faerie is a faeren.
Fat-Frank first appears in Dandelion Fire when Henry is taken by wizards and they are captured on the boat together. Monmouth frees them and together they take out the wizards. Fat-Frank helps Henry in getting to Hylfing because he is Mordecai's son and insists that Henry get christened as soon as possible. He tries to bring Henry directly to Hylfing by going through the faeren burrows, but other faeren take Henry to be put on trial for opening the cupboards. He is pronounced guilty and stuffed in their prison for further rulings on his punishment, but Frank Fat-Faerie along with two other faeries busts Henry out of jail. Then along with Monmouth, they rush through the burrows and come out near to Hylfing. They run for the city which is under attack by the wizards. As they near the city, they are attacked by wizards and the two other faeries are killed. Fat-Frank gives Henry a rough pep-talk and shoves him off into the harbor so that he can swim to the city and avoid being killed by wizards. Fat-Frank and Monmouth then somehow make it into the city and meet up with Henry and his family. During Henry’s christening, Fat-Frank tells Henry to throw the knife to break the curse holding Mordecai, Henry’s father, in a Faeren burrow.
In the Chestnut King, Frank Fat-Faerie is de-faeried by the faeren for giving away the secret of christening to Henry. (When Fat-Frank told Henry to throw the knife he broke their rules, and they were especially angry because then Mordecai was freed.) Fat-Frank is super depressed as he starts to lose his magic and turn to chalk. Mordecai asks Fat-Frank to stay and defend his home as a friend while Mordecai and Caleb travel to Endor. Fat-Frank gives his word. But just after they left, half the family is taken by soldiers from an envoy of ships. Fat-Frank runs with Henry to help, and on the way, he pranks some of the soldiers. But he does not succeed in finding the family. And while he and Henry searched, more soldiers came and took the children and Dotty from the house and left Henrietta and grandmother Anastasia in the burning house. Frank fights the soldiers and succeeds in saving little Anastasia, Richard and Una. There Fat-Frank receives a message by chestnut in which the Chestnut King claims him as his. Thirteen Faeren come to claim him, and take him, (along with Anastasia, Richard and Una) to the Chestnut king. Later, Henry joins them and convinces the king to come and fight Nimiane in exchange for Henry taking on the kingdom and letting the king go. Fat-Frank comes and fights alongside Henry, and is beside him when Henry finally destroys the witch. Fat-Frank had used up the last of his magic and was stiffening up, but Henry passes the kingship to Fat-Frank. He is crowned as the Chestnut King and regains his magic.