William Harvey (b. April 1, 1578) discoverer of the circulation of blood.
Two other Aries of note in the history of blood:
Joseph Lister (April 5, 1827) one of the greatest of 19th century surgeons, he performed thousands of amputations, and discovered antisepsis.
James B. Conant (March 26, 1893) a brilliant and creative polymath, president of Harvard University, began his professional life as a biochemist, and made significant contribution to the understanding of hemoglobin, and why blood is red.