It was known that Harry had a lightning-shaped scar on his forehead, which had become a hallmark of Harry. This is where Voldemort used the Requisition Charm to leave a lightning scar on his forehead.
Before she died, Harry's mother cast him an ancient protective spell, a magic of love, and Harry's mother, Lily, protected Harry with her life.
Because Voldemort had heard the prophecy that the boy named Harry was his mortal enemy, and when he tried to kill Harry, the protective charm took effect and consumed Voldemort, and Harry was attacked by Voldemort's requisite curse on his forehead, which caused a lightning-shaped scar. And Voldemort was also hurt because of this, and his vitality was greatly damaged.
In fact, it is also said that Voldemort deliberately left traces in order to find Harry for revenge in the future, which may be the reason why the lightning scar will become more and more painful when Voldemort recovers mana and approaches Harry.
As for why it is a "lightning" shaped marker, many friends have all kinds of wild ideas, Rowling explains: "Just because I am very stylish, I can't let my protagonist have a donut-shaped scar!."”