Evil Former Friend

This occurs whenever a good aligned character (sometimes The Hero, The Mentor, the Supporting Leader or the Big Good) is revealed to have had a history as friend, ally, mentor, or even student with a major villain.

Usually the friendship fell through simply because the future villain went power-mad and the other character didn't want any more to do with it, but more complex and unusual variations exist.

Sometimes it will be known all along, but sometimes it will be the subject of a dramatic reveal that can lead The Hero and the audience to reevaluate what they know about both characters. Note that this is about friends who turned evil in the Backstory and are either introduced or established in their first appearance as villains. If the friend turns evil over the course of the work, see Face–Heel Turn.

Examples

 * Professor X and Magneto in most versions of the X-Men.
 * Superman and Lex Luthor, in some versions.
 * Harvey Dent is shown as a close friend of both Batman and Commissioner Gordon before turning into Two-Face, particularly in The Long Halloween.
 * Black Mask and Hush were both Bruce Wayne's childhood friends, having turned into supervillains in their adult lives.
 * Reed Richards and Doctor Doom were college students who could only find intellectual debate and stimulation from each other, until Reed pointed out a mistake in Victor's schematics which was part of his last step in his Start of Darkness.
 * Toy Story 3: Lotso was this to Chuckles the Clown. Witnessing Lotso become a monster resulted in Chuckles becoming bitter and cynical.
 * In Coco, Hector and Ernesto de la Cruz used to be best friends and stage partners that would go on tour until Hector decided to quit show business and go back to his wife and daughter, which led to de la Cruz serving Hector a poisoned farewell drink, stealing Hector's song book and using it to become famous.