Leonard Miller

MC's father. Died in a plane crash six years before the story starts.
He and his wife fought a lot and MC and his sister were often sent to Allison's house for sleepovers to spare the kids the yelling and arguing.

It turns out that Leonard was the sperm donor used by Annabelle, thus Sophia is really MC's half-sister.

(His actual last name depends on the family name chosen for the Main Character, Miller is the default.)