It is known that James's parents were older when they had him, and Dorea would have been forty years old when she had a child if James was her son. However, it is also known that the Potters died of natural causes when they were old in wizarding terms, but Dorea Potter was only fifty-seven years old when she died, although, going by the ages that members of the Black Family - from which Dorea descended, did die - she lived to "old age" since most of them died in their fifties.
If Charlus and Dorea Potter were James's parents, James and his best friend Sirius Black would have been first cousins, once removed. Harry and Sirius, his godfather, would have been second cousins. Also, Harry's best friend/brother-in-law, Ron and wife, Ginny Weasley would be his third cousins. Harry would also be related, albeit distantly, to the Malfoys, Longbottoms, and Lestranges.
At the end of July in 1980, two infants were born matching this description: Harry Potter and Neville Longbottom. Voldemort went after Harry, resolving to kill him, and thus marked Harry as his equal, as the prophecy foretold. The Potters went into hiding through use of the Fidelius Charm, first choosing their close friend Sirius Black as Secret-Keeper, but Black persuaded the Potters to usePeter Pettigrew instead, thinking that this less obvious choice would further protect the Potters. Pettigrew, however, betrayed the Potters to Voldemort, who attacked the family in Godric's Hollow on 31 October, 1981. Voldemort slaughtered James and then Lily with the Killing Curse, but he first gave Lily the opportunity to save herself, at the request of Snape, who had been in love with Lily for years. When she refused, Voldemort killed her, unknowingly invoking ancient magic that protected Harry when Voldemort then attempted to murder him. The Killing Curse rebounded, leaving Harry its only known survivor and Voldemort temporarily defeated. The incident also caused a piece of Voldemort's soul to be embedded in the scar on Harry's forehead, inadvertently making him into a Horcrux.
Sirius soon discovered what had happened and pursued Pettigrew, who faked his own death and escaped. Sirius was subsequently framed and imprisoned in Azkaban for Pettigrew's crimes. Harry, who became known as "The Boy Who Lived" for his miraculous survival, was taken in by his mother's sister, Petunia Dursley, her husband Vernon and their son Dudley. Harry was raised in theMuggle world by the Dursleys, who treated him poorly and never told him about his wizarding heritage. Because they were blood relatives of his mother, however, Harry benefited from magical protections as long as he could call Number 4 Privet Drive "home."
Voldemort's inability to touch Harry, due to the lingering protection from his late mother, continued all the way up to his resurrection in 1995. Professor Quirrell, acting as host to Voldemort's soul, attempted to attack Harry to gain thePhilosopher's Stone in 1992, but was prevented from stealing the Stone when he came into contact with Harry's skin, leaving Voldemort forced to return to his non-corporeal state.
Voldemort eventually overcame this by using Harry's blood to regenerate his own body in 1995. Unbeknownst to Voldemort, this act also anchored Harry's life to his own. This was brought to light when Harry and Voldemort had their final confrontation in 1998 during the Battle of Hogwarts. Harry had spent almost a year destroying Voldemort's Horcruxes with his best friends Ron Weasley andHermione Granger, only to discover during the Battle of Hogwarts that he himself was a Horcrux Voldemort made accidentally that fateful Halloween night in 1981. Harry willingly stood before Voldemort and was struck with the Killing Curse. Because of this, the part of Voldemort's soul within him was destroyed. Because Voldemort had taken some of Harry's blood -- and thus Lily's blood, with its magical protections for Harry -- within himself, Harry survived the Killing Curse for a second time.
The two duelled one last time, and Harry defeated Voldemort once and for all.