The founder of physiology studies in Serbia and the pioneer of research on hypothermia, Ivan Djaja (Jean Giaja) was born 1884 to a French mother and a Serbian father, in L'Havre, France. Đaja gained his PhD at the Sorbonne in 1909. In 1910 he established the first Chair of Physiology in the Balkans and organized the first Serbian Institute for Physiology at the School of Philosophy of the University of Belgrade. He led this Institute for more than 40 subsequent years. His most notable papers were in the field of thermoregulation and bioenergetics.

Đaja became member of the Serbian academies of science and doctor honoris causa of Sorbonne. In 1952 for the seminal work on the behavior of deep cooled warm blooded animals he became associate member of the National Medical Academy in Paris. In 1955 the French Academy of Sciences elected him as associate member.

Đaja died in Belgrade, in 1957. Among colleagues he is fondly remembered by his golden DaVincian credo "Nulla dies sine experimento".

Alone, or with his co-workers, Đaja authored over 250 works, out of which about 200 were scientific. Rest of it includes popular, philosophical and children books. Critics say that "true word about Đaja, as a writer, still hasn't been said". Starting with his first non-scientific works published in the Srđ magazine, he was described as a natural born storyteller. His meditative prose is said to have a "specific place" in Serbian literature.

When he died, he left several writings with high literary merits in manuscripts: Conversations in Dubrovnik, short stories and his autobiography Discovery of the world.