Cedric Diggory (Alternate Timeline)

Normally a heroic character, in an alternate timeline created by the meddling of Albus Potter and Scorpius Malfoy, Cedric Diggory becomes a Death Eater and in fact is instrumental in helping to achieve victory for Voldemort and his followers, leading to a dystopian timeline.

history
This Cedric Diggory's history was the same as the "mainstream" Cedric Diggory up until Albus Potter and Scorpius Malfoy (time travelling to 1994 from over twenty years into the future), intervened in the second task to keep him from finishing it, hoping that in so doing they would save his life, which had been their entire motivation for going back in time in the first place. They succeeded, but unfortunately did so in such a way that Cedric Diggory ended up looking the fool in front of everyone assembled to watch for the second task. Seething with fury at his humilation, Cedric ended up joining the Death Eaters come Voldemort's return. As a result, during the Battle of Hogwarts, Cedric Diggory killed Neville Longbottom before he could destroy Nagini, thus keeping Voldemort immortal and allowing him to kill Harry Potter. This in turn condemned the Wizarding World to tyranny under Voldemort (and also caused Albus Potter to cease to exist).

Fortunately, Scorpius Malfoy was able to restore the timeline back to it's original form, and the Voldemort-run dystopia (and the Death Eater version of Cedric Diggory), seemingly ceased to exist.

trivia

 * The plot twist of Cedric Diggory becoming a Death Eater was panned by fans, who regarded it as an utterly absurd turn of events and even downright character assassination.
 * The idea of a normally heroic Harry Potter character becoming a Death Eater for petty reasons was previously done in many fan-fictions, usually with Ron Weasley being the one who becomes the Death Eater in question. This resemblance to that is likely an example of the common criticism about Harry Potter and the Cursed Child that it reads like, or resembles, "like bad fan-fiction".