American physician and member of the commission that proved that the infectious agent of yellow fever is transmitted by a mosquito, later known as Aëdes aegypti.

Lazear received his medical degree (1892) from the College of Physicians and Surgeons of Columbia University. After a period of study in Europe, he joined the staff of Johns Hopkins Hospital, Baltimore, where he was among the first to investigate the structure of the malarial parasite. In 1900 he went to Cuba as a surgeon with the U.S. Army. There he was asked to join the yellow-fever commission, which included Walter Reed, James Carroll, and Aristides Agramonte. In the course of his research he was bitten by a mosquito, contracted yellow fever, and died.