Final answer:
The Tarasoff v. Regents of the University of California case established the 'duty to warn' mandate for therapists to protect individuals from threats of bodily harm made by a patient.
Step-by-step explanation:
The legal case that led to the decision mandating therapists to make all efforts to prevent danger to another or to self, also known as the "duty to warn," is a) Tarasoff v. Regents of the University of California. This pivotal case occurred in 1976 when the Supreme Court of California ruled that mental health professionals have a duty to protect individuals who are being threatened with bodily harm by a patient. This includes warning the potential victim and notifying the police about the threat. This decision established legal expectations for therapists and other mental health professionals regarding the limits of confidentiality and their obligations to third parties.