Laika was one of the Russian space dogs and the first living passenger to enter orbit on Sputnik 2, a Soviet spacecraft. Some classify her as the first animal to enter space, although others argue that animals had entered space during sub-orbital flights on previous missions.

Laika was found as a stray wandering the streets of Moscow, a female part-Samoyed terrier weighing approximately 6 kg (13 lb) and about 3 years old. Her name was changed from Kudryavka (Russian for "Little Curly"), and she was nicknamed Zhuchka ("Little Bug") and Limonchik ("Lemon"). The American press dubbed her Muttnik (a portmanteau of mutt and Sputnik).

Laika died on November 4, 1957, a few hours after launch from stress and overheating. Her true cause of death was not made public until years after the flight, with officials always stating that she was either euthanized by poisoned food or died when the oxygen supply ran out. Russian officials have since expressed regret for allowing Laika to die; to this date, Laika is the only living passenger ever to have been launched into space without the intention of retrieval.

Sputnik 2 was not designed to be retrievable, so Laika was doomed to die from the beginning.