Matthew Chase

Matthew Chase is Mr. and Mrs. Chase's son and Annabeth Chase's younger half-brother. His father confuses him with his identical twin brother, Bobby Chase.

History
Matthew and Bobby were born to Mr. and Mrs. Chase during the 1990s. Due to his half-sister, Annabeth, was a demigod and monsters would frequently attack her and her family, Annabeth felt she needed to run away when Matthew was just a baby.

The Titan's Curse
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."

Frederick Chase
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 both care for their father.

Mrs. Chase
She is the mother of Bobby and Matthew and the step-mother of Annabeth.

Annabeth Chase
Matthew's and Bobby's half-sister.

Bobby Chase
Bobby is Matthew's twin brother and the family has a hard time distinguishing one from another.