Matthew and Bobby were born to Mr. and Mrs. Chase during the 1990s. Due to his half-sister, Annabeth being a demigod, monsters would frequently attack her and her family. Annabeth felt she needed to run away when Matthew was just a baby.
He is seen with his family on Half-Blood Hill waiting to pick up his half-sister.
He is playing with his brother, Bobby Chase when Percy Jackson, Thalia Grace, Grover Underwood, and Zoë Nightshade ask Mr. Chase, Annabeth's mortal father, for help. Percy looks at the Lego toys scattered on the floor and the cookies in the oven and decides it's "not a bad place."
He and Bobby are mentioned when his half-sister is recalling her childhood of being attacked by spiders.
Demonstrated in The Titan's Curse, Frederick Chase, the father, does not pay attention to Bobby and Matthew while at work. However, both Matthew and Bobby care for their father.
She is the mother of Bobby and Matthew and the step-mother of Annabeth.
Matthew's and Bobby's half-sister. Annabeth dislikes him, and considers him to be her step-brother.
Bobby is Matthew's twin brother; the family has a hard time distinguishing one from another.