Eric Masterson was an architect that became friends with Thor when he occupied the identity of Sigurd Johnson. After Eric was badly wounded trying to help Thor fight Mongoose, Thor asked Odin to merge their life forces. The end result was two men within one body. They often fought of control over the body, and eventually Eric lost custody of his son Kevin because of his absences.

After Loki was thought to have been slain by Thor, Odin banished him, and Thor's power was bestowed upon Masterson. Although he tried to hide it, Eric's inexperience soon showed. However, Masterson began to master his new abilities and soon replaced Thor in the Avengers. Odin finely freed Thor form banishment, and thought it best for Eric to stay as his replacement, but Odin eventually made Eric his own weapon, a mace called Thunderstrike.

Because he could think of nothing better to call himself, he took the alias Thunderstrike. He then found that the powers of the Thunderstike were different form those of Mjolnir. After he found out that the powerful villain Bloodaxe was really his girlfriend Jackie Lukas, he took the Bloodaxe and used it along with the Thunderstike Mace to kill Seth, the Egyptian god of death. However, he was corrupted by the power of the Bloodaxe and went on a rampage. After battling Thor, Eric regained control and turned the Thunderstrike against the Bloodaxe killing him in the process. Thor wanted his best friend to go to Valhalla for his heroism, but Eric said he was a man first and a hero second, and was sent by Odin to his own afterlife. On his gravestone Thor wrote "THE WORLD STILL NEEDS HEROES."