Final answer:
Harry was told by the Dursleys that his parents died in a car crash, a lie to cover up their magical heritage and the true cause of their death by Voldemort's curse.
Step-by-step explanation:
The Dursleys told Harry that his parents died in a car crash. This fabricated story was intended to hide the truth about their magical background and their actual cause of death, which was a result of the curse by the dark wizard, Voldemort. In the 'Harry Potter' series, this lie is a key point of Harry's early life, and it shapes his understanding of his parents until he enters the wizarding world and learns the truth.