Zvonimir Janko

Zvonimir Janko (1932 to 2022) was a Croatian mathematician who gave his name to the Janko groups, sporadic simple groups in finite group theory. Born in Bjelovar, he studied at the University of Zagreb and took his doctorate there in 1960 under Vladimir Devide, solving a problem posed by Laszlo Redei. After teaching physics at a school in Siroki Brijeg he left Yugoslavia in 1962 for Australia, taught at Monash University and became a professor at the Australian National University in 1964. He later held posts at Princeton and Ohio State and, from 1972 until his retirement in 2000, at Heidelberg University. In 1964 he constructed the group now called J1, the first new sporadic simple group found after the Mathieu groups, nearly ninety years after the last of those was discovered. This launched the modern theory of sporadic groups and was an important step toward the classification of finite simple groups. He predicted J2 in 1966 and J3 followed, and in 1975 he found J4, which was confirmed by computer calculation in 1980.