universal donor

from WordNet (r) 3.0 (2006)

universal donor
    n 1: a person whose type O Rh-negative blood may be safely
         transfused into persons with other blood types

from The Collaborative International Dictionary of English v.0.48

Universal donor \U`ni*ver"sal do"nor\, n. (Med.)
   a person belonging to the O blood group (of the ABO
   classification), who can safely donate blood to anyone.
   [PJC]