a person who gives or donates.

Medicine/Medical . a person or animal providing blood, an organ, bone marrow cells, or other biological tissue for transfusion or transplantation.

Law . a person who gives property by gift, legacy, or devise, or who confers a power of appointment.

of or pertaining to the biological tissue of a donor

donor organ.

noun

almsgiver , altruist , angel * , backer , benefactor , benefactress , bestower , conferrer , contributor , donator , grantor , heavy hitter * , patron , philanthropist , presenter , santa claus * , savior , subscriber , giver , humanitarian