The rottenweiler in my old hood was a jackass. It killed woodchucks and chased cats and just sort of menaced everyone.
Mine would go after someone if I said the words, but otherwise she was a big baby. She guarded Murray and Chloe (the original G's) and Murray would even complain until she greeted him in the morning.

Was friendly to the UPS guy and would sit on his foot until he stopped petting her or gave her whatever package he was bringing to us. Defect rolled in like he owned the joint.
In contrast, her mom was put down for being aggressive and biting kids. I think it's 50/50 with dogs. Kind of like people. Genes are half of it, conditioning is the other half.