The Changeling was an enemy of Conan the Barbarian.
The alien that would impersonate Conan lived in a planet a vast distance from Earth. Its world and environment was very different than Earth. It violated the law of its society and did not want to face the dire consequences of its actions, and so left its world in a spaceship. It arrived on Earth in the Hyborian Era and quickly discovered that it couldn't breathe the air, but it had a device that enabled it to assume the form of a human being and thus live for a few days more. Many times, its gemstone let the changeling assume the form of several men, although this killed them, until it assumed the form of Warz Bel Doqh.
After having killed the real Warz Bel Doqh in his house, a band of cutthroats assaulted the house and Zareg stole his gemstone. Conan found the transformed Changeling in the middle of the smoke and flames, and agreed to help find the criminals in exchange for half of his riches. During their journey, they met Purani, a tavern girl, and had to fight and avoid the Zingaran squadrons sent by Phor-Thok to kill Conan. Across Stygia and Kush, the false Warz Bel Doqh became weaker and weaker, but when some yellow-eyed ghouls attacked the group, he saved Conan. The Changeling's alien presence scared the ghouls and they ran away.
The Changeling was saved again by Conan when the cannibals attacked them until they reached Zareg, the thief who had the gemstone. In a cavern under a waterfall, while Conan fought a giant spider, the alien picked up the gemstone, and regained its strength. Conan won the battle with the spider, only to be unkindly thanked by the alien with the stealing of his lifeforce. The Changeling assumed the protoplasmic form of Conan leaving the Cimmerian weak with only few minutes to live. The Conan protoplasm left the cavern but was captured by a Zingaran squadron of soldiers. The transformed Changeling was immediately executed. The soldiers went away, sure that they had fulfilled their mission for the King of Zingara. However, away from the action, the real Conan recovered completely. After the alien's death, Conan's lifeforce had returned to him.