Thor, Vol. 1 #276 (1978)

Mine, This Hammer
Loki prompts Red to put on Thor's Belt of Strength. Red goes to Bilskirnir while the trial of Loki begins. Red steps into the Fire of Geirrodur with the Belt and gloves and gains the power of Thor. Red then breaks in and attacks Thor, taking Mjolnir from him. Odin tells everyone to not interfere. Red and Thor battle with Red getting the better of him. As Red is about to deliver the death blow, Joey jumps between them, resulting in his death. Red tells Sif that she either comes away with him, or he destroys the shield around Balder, and she has no choice.
Release Date: 1978