Andrew Mulligan is Little Bill's best friend and he loves to have fun. Andrew is a 5-year-old boy. When Andrew's family moved two doors down from Little Bill, they became fast friends. Andrew is as good at playing make-believe as Little Bill, and both boys share a love of adventure and Captain Brainstorm. Andrew has two older cousins, 11-year-old Rachel and 13-year-old Kevin, who sometimes visit and play with Little Bill, April, and Bobby. He likes Captain Brainstorm like Little Bill does
Andrew is a ginger, he is always picked on and does far from excelling when it comes to anything physical.