  We construct and discuss a toy model of the population of numerous
non-identical extragalactic sources of ultra-high-energy cosmic rays. In the
model, cosmic-ray particles are accelerated in magnetospheres of supermassive
black holes in galactic nuclei, the key parameter of acceleration being the
black-hole mass. We use astrophysical data on the redshift-dependent black-hole
mass function to describe the population of these cosmic-ray accelerators, from
weak to powerful, and confront the model with cosmic-ray data.
