An individual who donates blood on his own volition or initiative and without monetary compensation is called:

A voluntary blood donor is someone who willingly decides to donate blood without any form of compensation, including monetary rewards. This type of donation is highly encouraged as it tends to result in fewer health risks for both the donor and the recipient, promotes a sense of community, and supports the blood supply in a safe and ethical manner.

In contrast, the terms for the other types of donors highlight different motivations or contexts that do not align with the concept of voluntary donation. A walking blood donor usually refers to someone who is easily accessible for immediate donation, possibly in emergency scenarios, but does not specifically denote the lack of compensation. A remunerated blood donor is, by definition, compensated for their donation, which directly conflicts with the idea of voluntary donation. An ambulatory blood donor typically describes the physical condition of the donor—being able to walk or move around—rather than their motivation for donating blood. Thus, the best term to describe someone who donates blood of their own accord, without expecting anything in return, is indeed a voluntary blood donor.