Zygophyseter varolai is an extinct, primitive sperm whale. The common name of "killer sperm whale" refers both to its relation to modern day sperm whales, and to its similarity in size to and its "probable similar feeding adaptation to the extant delphinid killer whale (Orcinus orca)".
Its fossil, an almost complete skeleton, dates from the Tortonian Age of the Late Miocene Epoch of Southern Italy. It has a very long zygomatic process, probably for housing the spermaceti organ. Z. varolai has a large body size with large teeth present in both jaws making it capable of feeding on large prey.