Joseph is the biological father of David.
Joseph Strorm is a strict disciplinarian, and David knows this. Despite knowing that his dad is adamant about adhering to religious rules of Waknuk society, David still makes mistakes. Those mistakes really bring out the true nature of the relationship between David and his dad. For example, Joseph became enraged and accused David of blatantly calling upon the Devil to give him another hand. In reality all David was asking for was a little extra help.
"You — my own son — were calling upon the Devil to give you another hand!" he accused me.
"But I wasn't. I only —"
"Be quiet, boy. Everyone in this room heard you. You'll certainly make it no better by lying."
I don't believe there is much compassion and love within the relationship. Joseph treats his family in the exact same way that he treats the rest of the Waknuk people that he helps govern.
Despite having Joseph as a father, David grows up to be an incredibly patient and compassionate person. Perhaps it is because David sees how his father treats people, and David unconsciously decides that he will never be like that. I believe that is why David admires his Uncle Axel so much.