Draco Black
Before Draco took the dark mark he found out the man who he thought was his father is not. In fact what throws off Draco more is the true identity of his father, Regulus Black. What?! Well the circumstances are that Narcissa Malfoy nee Black was not a born Black but rather a Rosier. Narcissa was born to the brother/sister of Druella. After Druella's brother/sister died Druella took baby Narcissa in, which is the reason why she looks Rosier than Black unlike Andromeda and Bellatrix. It was agreed that the Wizarding World would know that Cygnus and Druella Black had three daughters instead of just two. Narcissa was raised as a Black even though she was told by Cygnus at a young age she wasn't. When Narcissa married Lucius Malfoy it had became clear that Lucius was sterile due to a curse from a muggleborn he had tortured. With the help of Bellatrix, Regulus was put under the imperius curse and had sex with an equaly imperio'd Narcissa. After the deed was done Lucius obliviated the event from both Regulus and Narcissa's memories. Nine months later Draco was born, by then Regulus had died when he found out about his son and was killed by Voldemort who discovered Regulus took the necklace. Draco angered by the lies from Lucius and the injustice done to his mother decided to finish his real father's mission to destroy the horcruxes. If Potter and his posse could stay out of his way.