In the context of body donation, an individual who makes a legacy of their body is referred to as:

The term "donor" specifically refers to an individual who voluntarily gives their body or body parts for the purpose of medical research, education, or organ transplantation after their death. In the context of body donation, the individual is making a significant contribution to science, helping to advance medical knowledge and training by allowing their body to be used for study and educational purposes.

This term emphasizes the altruistic nature of body donation, highlighting the individual's intention to provide a lasting legacy that benefits humanity, particularly in the fields of medicine and science. The process typically involves legal documentation and consent, where the individual or their family expresses their wishes to donate the body for these purposes.

The other terms do not encapsulate the essence of body donation: a "decedent" simply refers to a deceased person, a "testator" is someone who prepares a will, indicating wishes for the distribution of their property after death, and a "legatee" is a person who receives a legacy under a will. None of these terms specifically denote the act of donating one's body for educational or research purposes.