Reuben Ottenberg (1882, New York City - 1959) was an American physician and haematologist, who served Mount Sinai Hospital in New York City with distinction for 50 years.
He received his B.A. from Columbia University in 1902 and his M.D. degree from the College of Physicians and Surgeons three years later.
He published his groundbreaking paper on blood transfusion before World War I. In haemocompatibility tests, which he had started in 1907  he found out that patient antibodies against donor red cells could be harmful but not vice versa. This report led to the use of group O (“zero”) individuals as universal donors.
In 1954 Ottenberg was the first to be awarded the Karl Landsteiner Award from the American Society of Blood Banks for "distinguished pioneering contributions to blood banking and hemotherapy."
- ^ online biography
- ^ haemocompatibility tests
- ^ List of Karl Landsteiner Award recipients