Cas has been Ellie's best friend since they were kids. He goes by Cas because he feels like Casey is such a girly name. He cares about her a lot and often worries about her wellbeing. He knows her very well and can read her better than anyone else. He'd do literally anything for her. He's sort of a slob since his mom is rarely home and he has the house to himself a lot, so Ellie often finds herself picking up after him when he comes over. He also makes a lot of movie references... mostly to kids movies. He's also very intelligent and tends to pick up on things quickly.

His voice is more mid-pitched than anything.