Zvonimir Janko (born in 1932 in Croatia), studied mathematics and earned his PhD at the University of Zagreb. He is professor of mathematics at the University of Heidelberg, Germany, and his name is well known among experts in the theory of finite groups. Professor Janko discovered sporadic groups named J₁, J₂, J₃, and J₄ in his honour. They are called Janko groups.

Zvonimir Janko in 2007, at the age of 75
(photo by dr. Mario Pavcevic, Zagreb)

The discovery of J₁ in 1964, more than a century after the discovery of the first sporadic group, launched the modern theory of sporadic groups. His group J4, discovered in 1976, has

86 775 571 046 077 562 880

elements. About his research he delivered an invited lecture at the International Congress of Mathematicians in Nice, France, 1970.

• A.A. Ivanov (professor at Imperial College, London): The Fourth Janko Group (256 pp), Oxford Math. Monographs, 2005.
• Janko Groups at Wolfram MathWorld
• Janko Groups at Wikipedia