Kairuku grebneffi is an extinct species of giant penguin. It is among the tallest and heaviest penguins attested to, weighing 50% more than modern emperor penguins. The species is marked by a slender body and long, slender beak. K. grebneffi lived in what is now New Zealand during the late Oligocene, going extinct around 25 million years ago. The first bones of the species were discovered in 1977, but it was not classified as a distinct species until 2012.