William Osler was a Canadian physician considered to be one of the most influential figures in the history of medicine. He is regarded as the greatest physician in the entire English-speaking world, and was equally famous as a writer, medical philosopher, historian, teacher and a practical joker. Initially intending to join the clergy, he changed his stream while studying at Trinity College Toronto. Subsequently, he earned his medical degree from McGill University, Montreal, before undertaking his postgraduate studies in Europe. Thereafter, he began his career at McGill University as an instructor, becoming full professor within a year. Very soon, his fame spread all over North America, and he was invited to join University of Pennsylvania as professor of clinical medicine. After four years there, he joined Johns Hopkins Hospital as one of its founding professors, playing a pivotal role in turning it into one of the best hospitals. Later, he moved to Oxford as Regius Professor of Medicine, retaining the position until his death at the age of seventy. Although he spent bulk of his career in USA and England, he remained a Canadian citizen throughout his life.