Neville Longbottoms parents were well-respected Aurors and members of the original Order of the Phoenix. They were tortured into insanity by Death Eater Bellatrix Lestrange for so long that they lost their minds. Following the hospitalization of his parents, Neville Longbottom was sent to live with his grandmother, Augusta. Nevilles grandmother was very protective of him, but he didnt have the emotional support that was necessary to make real friends or meaningful relationships. Nevilles parents torture was a huge influence over his early life, and he lost all his confidence and self-assurance, which is why he was such a timid and shy boy in the first few books/movies. Nevilles parents were never killed, but they arguably suffered something worse.