Karla Sofen

Two Marvel Comics characters have been named "Moonstone".

The first Moonstone was a Captain America villain affiliated with the Secret Empire. He was empowered by a stone found in the Moon's surface, hence his codename. After the Secret Empire's defeat he was arrested, and eventually had his alien gem stolen from him by Karla Sofen, who became the second Moonstone. He later turned up again with ionic powers and the new codename "Nefarius".

Karla Sofen, the second Moonstone, has had a far longer and more complex career as both a villain and heroine, often alongside teams such as the Masters of Evil and the Thunderbolts. Her power levels raised drammatically once she absorbed a second alien gem, but as of 2004's "Avengers/Thunderbolts" limited series she lost both gems to Baron Zemo and when last seem was comatose.