Jem and Scout’s mother died when Scout was young, and they were raised by their father Atticus.
In the first chapter, we learn Scout’s back story. Scout comments that Calpurnia has been with them since Jem was born, but she is the only mother figure.:
“Our mother died when I was two, so I never felt her absence.” (ch 1)
Scout comments that Jem remembers their mother, and sometimes gets sad and distant when he thinks of her.
Atticus was already older when he married. He is described as being middle aged when Scout was born. So he is an older man trying to raise two children on his own. Scout has this to say about her father.
Jem and I found our father satisfactory: he played with us, read to us, and treated us with courteous detachment. (ch 1)
Atticus is a hard-working lawyer, and a supremely moral man. He teaches his children empathy, and makes sure they know they are no better than anyone else. He makes sure they don’t discriminate for race or class. Although his children are somewhat embarrassed by him as the book begins because of his age, they gain new respect for him first when he shoots the mad dog, and then after the trial.