Stjepan Mohorovičić

Stjepan Mohorovičić (August 20, 1890 - February 13, 1980) was a Croatian scientist (physicists and geophysicist) born in the town of Bakar and died in the city of Zagreb, Croatia. His father is the world-famous geophysicist Andrija Mohorovičić.

Stjepan Mohorovičić is often called "the father of positronium" because his most significant work is the prediction of the existence of positronium. Positronium is the bound state of an electron and a positron (anti-electron) and therefore the lightest atom. Mohorovičić's prediction of positronium was published in 1934 in the prominent German scientific journal Astronomische Nachrichten, where it was called "electrum". It was experimentally discovered by Martin Deutsch in 1951 and became known as positronium.