Most Rottweilers have protective instincts toward strangers. They need extensive exposure to friendly people so they learn to recognize the normal behaviors of "good guys." Then they can recognize the difference when someone acts abnormally. Without careful socialization, they may be suspicious of everyone, which could lead to biting. Some Rottweilers go in the opposite direction -- without enough socialization, they become fearful of strangers, which can lead to defensive biting.
Many Rottweilers will not tolerate another dog of the same sex, and some won't tolerate the opposite sex either. Some Rottweilers have strong instincts to chase and seize cats and other fleeing creatures. If anything goes wrong in the breeding, socializing, training, handling, or management of this breed, it is capable of seriously injuring or killing other animals.
Rottweilers are not Golden Retrievers. The best Rottweilers are versatile working dogs, capable of learning a great deal, but they are not pushovers to raise and train. Some Rottweilers are willful, obstinate, and dominant (they want to be the boss) and will make you prove that you can make them do things. You must show them, through absolute consistency that you mean what you say.