Konrad Zacharias Lorenz (Austrian German pronunciation: [ˈkɔnʁaːd tsaxaˈʁiːas ˈloːʁɛnts] ^ⓘ; 7 November 1903 – 27 February 1989) was an Austrian zoologist, ethologist, and ornithologist. He shared the 1973 Nobel Prize in Physiology or Medicine with Nikolaas Tinbergen and Karl von Frisch. He is often regarded as one of the founders of modern ethology, the study of animal behavior. He developed an approach that began with an earlier generation, including his teacher Oskar Heinroth.

Lorenz studied instinctive behavior in animals, especially in greylag geese and jackdaws. Working with geese, he investigated the principle of imprinting, the process by which some nidifugous birds (i.e. birds that leave their nest early) bond instinctively with the first moving object that they see within the first hours of hatching. Although Lorenz did not discover the topic, he became widely known for his descriptions of imprinting as an instinctive bond. In 1936, he met Tinbergen, and the two collaborated in developing ethology as a separate sub-discipline of biology. A Review of General Psychology survey, published in 2002, ranked Lorenz the 65th most cited scholar of the 20th century in the technical psychology journals, introductory psychology textbooks, and survey responses.

Lorenz's work was interrupted by the onset of World War II and in 1941 he was recruited into the German Army as a medic. In 1944, he was sent to the Eastern Front where he was captured by the Soviet Red Army and spent four years as a German prisoner of war in Soviet Armenia. After the war, he regretted his membership in the Nazi Party.

Lorenz wrote numerous books, some of which, such as King Solomon's Ring, On Aggression, and Man Meets Dog, became popular reading. His last work Here I Am – Where Are You? is a summary of his life's work and focuses on his famous studies of greylag geese.

Lorenz was the son of Adolf Lorenz, a wealthy and distinguished surgeon, and his wife Emma (née Lecher), a physician who had been her husband's assistant. The family lived on a large estate at Altenberg, and had a city apartment in Vienna. He was educated at the Public Schottengymnasium of the Benedictine monks in Vienna.

In his autobiographical essay, published in 1973 in Les Prix Nobel (winners of the prizes are requested to provide such essays), Lorenz credits his career to his parents, who "were supremely tolerant of my inordinate love for animals", and to his childhood encounter with Selma Lagerlöf's The Wonderful Adventures of Nils, which filled him with a great enthusiasm about wild geese."

At the request of his father, Adolf Lorenz, he began a premedical curriculum in 1922 at Columbia University, but he returned to Vienna in 1923 to continue his studies at the University of Vienna. He graduated as Doctor of Medicine (MD) in 1928 and became an assistant professor at the Institute of Anatomy until 1935. He finished his zoological studies in 1933 and received his second doctorate (PhD).

While still a student, Lorenz began developing what would become a large menagerie, ranging from domestic to exotic animals. In his popular book King Solomon's Ring, Lorenz recounts that while studying at the University of Vienna he kept a variety of animals at his parents' apartment, ranging from fish to a capuchin monkey named Gloria.