The guardian of Mary and Henry, he's generally considered to be a bad influence and his home is presented as a bad place to raise the young Mary and Henry. The Admiral invited his mistress to move in with him after his wife, Mrs. Crawford, died. Mary quickly moved out of his house after that. Though she doesn't think fondly of the Admiral, Henry appears to get along well with him. The Admiral's conduct may very well have been a negative influence on Henry. The Admiral does help get William his promotion, though, and ultimately it's never made entirely clear what sort of man he is since Mary and Henry have divided opinions on the subject and since we only have their words to go on here.