Magneto- Classic X-Men #12
In Classic X-Men #12 flashbacks show Magneto, still known as Max Eisenhardt, living with his wife Magda and their daughter Anya. Max is working as a laborer and is angered by his unfairly low wage. During an argument, Max uses his innate power to hurl a crowbar at his boss.
Max is shocked at his newfound ability to create/control magnetic fields. He flees from his place of work and heads home to find that his house is on fire- with his family still inside. Max manages to save his wife but his daughter, Anya, dies in the fire.
In his emotional state, Max loses control and blacks out. Max wakes up to discover that, in his rage, he killed every person living in their village by shooting lightning from his eyes. His wife, Magda, is terrified of him and runs away.