  Intracluster medium (ICM) abundances are higher than expected assuming
enrichment by supernovae with progenitors belonging to the simple stellar
population (SSP) observed in cluster galaxies, if stars formed with a standard
initial mass function (IMF). Moreover, new results on ICM oxygen abundances
imply that nucleosynthesis occurred with nonstandard yields. The hypothesis
that hypernovae (HN) in general, and HN associated with Population III (Pop
III) stars in particular, may significantly contribute to ICM enrichment is
presented and evaluated. The observed abundance anomalies can be explained by a
hypernovae-producing subpopulation of the SSP, but only if it accounts for half
of all supernova explosions and if Type Ia supernova rates are very low. Also,
the implied energy release may be excessive. However, an independent Pop III
contribution -- in the form of metal-free, very massive stars that evolve into
hypernovae -- can also account for all the observed abundances, while avoiding
these drawbacks and accommodating a normal IMF in subsequent stellar
generations. The required number of Pop III stars provides sufficient energy
injection (at high redshift) to explain the ICM ``entropy floor''. Pop III
hypernova pre-enrich the intergalactic medium, and can produce a significant
fraction of the metals observed in the Lyman-alpha forest. Several testable
predictions for ICM and IGM observations are made.
