Haast's eagle is an extinct species of eagle that lived in the South Island of New Zealand, commonly accepted to be the pouākai of Māori mythology. It is the largest eagle known to have existed, with an estimated weight of 10–18 kilograms, compared to the next-largest and extant harpy eagle, at up to 9 kg (20 lb). Its massive size is explained as an evolutionary response to the size of its prey—the flightless moa—the largest of which could weigh 200 kg (440 lb). Haast's eagle became extinct around 1445, following the arrival of the Māori, who hunted moa to extinction, introduced the Polynesian rat, and destroyed large tracts of forest by fire.

Extinction is the termination of a taxon by the death of its last member. A taxon may become functionally extinct before the death of its last member if it loses the capacity to reproduce and recover. Because a species' potential range may be very large, determining this moment is difficult, and is usually done retrospectively. This difficulty leads to phenomena such as Lazarus taxa, where a species presumed extinct abruptly "reappears" after a period of apparent absence.