One of the more frequently invoked narratives in fiction for purposes of drama is the hero who must do battle with a villain who also happens to be their friend. The source of the confrontation may vary, perhaps their friend is possessed/brainwashed, perhaps both still care for each-other but just have philosophical differences, perhaps they consider each-other worthy adversaries, perhaps one has always been good and the other always evil but they enjoy each-other's company despite their difference, or maybe they were once friends before becoming enemies but with the hero holding out hope they can be again. Whatever the case when the two actually come to blows it is almost always centered as a significant fight for both parties. These are such heroes, protagonists who need to fight those near and dear to them, whether such friendships can be maintained in spite of the fight or if the villain can be redeemed varies from work to work.
IMPORTANT: this category is only for heroes who were (or even still are) genuinely friends with the villain/villains. Faked friendship for manipulation or other goals is NOT ACCEPTED.