Gekko gecko, commonly known as the Tokay Gecko, is a nocturnal arboreal gecko native to tropical Asia. They are abundant, ranging from northeast India and Bangladesh, throughout Southeast Asia, to Indonesia and western New Guinea. Naturalized populations (introduced via the pet trade) are also found in Florida and Hawaii in the United States. Their native habitat is rainforest trees and cliffs, and they also frequently adapt to human habitations, roaming walls and ceilings at night in search of insect prey.

Tokays are among the largest of the geckos, attaining lengths of about 30-40cm (males), 20-30cm (females) and weights of 150-300g. They are distinctive in appearance, with a bluish or grayish body sporting orange or red spots.

They are renowned for their aggressive disposition and their loud vocalizations (unusual for lizards). Their mating call, a loud croak, is variously described as sounding like tokeh or gekk-gekk, whence both the common and the scientific name (deriving from onomatopoeic names in Malay or Javanese), as well as the family name Gekkonidae and the generic term gecko. United States soldiers in Vietnam, notoriously, interpreted the nighttime calls of the local tokays as sounding like "f**k you" and gave the gecko the nickname f**k-you lizard, a sobriquet which might also appropriately describe the lizards' attitude towards a perceived predator: when threatened, rather than attempting to escape, they open their mouth in a wide gaping display, and they do not hesitate to bite. The bite of a large tokay, while unlikely to cause lasting damage to a human, is painful and can easily draw blood. Furthermore, a tokay gecko, once having bitten, will not readily let go. Tokay owners report that the only effective way (other than waiting) to get the lizard to release its hold is to submerge it in water!

Despite their unpleasant disposition, tokays have been popular in the pet trade. (Their popularity, in the United States at least, has waned somewhat in recent years.) They are abundant and inexpensive (most specimens sold are wild-caught), make a spectacular display animal (although, being nocturnal animals, they are not very active in the daytime), and are not difficult to maintain or breed, so long as they are given a sufficiently large enclosure (which should be vertically oriented). They may be fed insects and small ("pinky") mice. Some owners report that they have "tamed" their tokays to the point that they can handle them, but for the most part these lizards do not take well to being handled, unlike (for instance) the popular leopard gecko.

Pet shop owners in New York City have been known to recommend the tokay gecko to apartment dwellers there as a means of keeping the perennial cockroach problem under control. While there is no doubt that a freely-roaming tokay will make a dent in the household insect pest population (as they do in Southeast Asia, where they frequently live in human habitations), there are a few disadvantages to this approach. For one, if pesticides have been used in an attempt to exterminate the insects, these may be ingested by the lizard and cause it harm. Also, especially if a breeding pair of geckos is present, the loud mating calls can be quite disturbing to the apartment's human occupants! Finally, there is the problem of gecko droppings ending up behind furniture and in other obscure places.