The dog Laika was the first Earthling to go into orbit. It wasn't revealed at the time that she died early on in the mission.
In 1998, after the collapse of the Soviet regime, Oleg Gazenko, one of the scientists responsible for sending Laika into space, expressed regret for allowing her to die:
Work with animals is a source of suffering to all of us. We treat them like babies who cannot speak. The more time passes, the more I'm sorry about it. We shouldn't have done it ... We did not learn enough from this mission to justify the death of the dog.
Laika has a little memorial - a model dog standing atop a rocket near a military research facility in Moscow.