Dafydd "David" Rhys Williams[1] (born May 16, 1954)[2] is a Canadian physician, public speaker, author and retired CSA astronaut.

[3] Williams received postgraduate training in advanced invertebrate physiology at the Friday Harbor Laboratories of the University of Washington.

While working in the Neurophysiological Laboratories at the Allan Memorial Institute for Psychiatry, he assisted in clinical studies of slow wave potentials within the central nervous system.

[3] His clinical research in emergency medicine has included studies evaluating the initial training and skill retention of cardiopulmonary resuscitation skills, patient survival from out-of-hospital cardiac arrest, the early identification of trauma patients at high risk, and the efficacy of tetanus immunization in the elderly.

In addition, he has trained ambulance attendants, paramedics, nurses, residents, and practicing physicians in cardiac and trauma resuscitation as a course director in Advanced Cardiac Life Support (ACLS) with the Canadian Heart and Stroke Foundation and in Advanced Trauma Life Support (ATLS) with the American College of Surgeons.

In 1990, he returned to Sunnybrook as medical director of the ACLS program and coordinator of postgraduate training in emergency medicine.

He completed basic training, and in May 1993 was appointed manager of the Missions and Space Medicine Group within the astronaut program.

During this CAPSULS Project he was the Principal Investigator of a study to evaluate the initial training and retention of resuscitation skills by non-medical astronauts.

His other oversight responsibilities were in the fields of telemedicine, 3-D tissue culture/regeneration in microgravity, the curatorial management of extraterrestrial materials, and of qualifying humans for very long space journeys and ensuring their safe return to Earth.

Williams served as an aquanaut on the first NEEMO (NASA Extreme Environment Mission Operations) crew aboard the Aquarius underwater laboratory in October 2001.

During this eighteen-day mission, the six-person crew developed lunar surface exploration procedures and telemedical technology applications.

In 1983, he also received the psychiatry prize and the Wood Gold Medal for clinical excellence from the Faculty of Medicine and was named on the dean's honor list by the physiology department, at McGill University, for his postgraduate research.

[3] He was twice awarded the second prize for his participation in the University of Toronto Emergency Medicine Research Papers Program, in 1986, and 1988,[3] and received top honours in that competition in 1987.

[citation needed] Following STS-90, in 1999, he received the Melbourne W. Boynton Award from the American Astronautical Society and the Bronze Medal from the Spanish Council for Scientific Research (CSIC).