Zvonimir Janko (born 1932) is a Croatian mathematician who is the eponym of the Janko groups, sporadic simple groups in group theory.
Janko was born in Bjelovar, Croatia. He studied at the University of Zagreb where he received Ph.D. in 1960. He then taught physics at a high school in Široki Brijeg in Bosnia and Herzegovina. Later he worked as a professor at the University of Zagreb, the University of Heidelberg, Monash University, and at the Australian National University.