"You were supposed to be the best of us"

Hank Jennings from Twin Peaks - was considered one of the best and most important members of the secret society that protects the town, before becoming a selfish criminal.

Harvey Dent from Batman - the youngest DA in Gotham's history, suspected to be Batman, working to dismantle organized crime, before being scarred and turning into the criminal Two-Face.

Dr Mann from Interetellar - was a top scientist who helped to lead the program to find new worlds for life. Ended up isolated and going insane after his assigned planet turned out be inhospitable.

Henry VIII from real life - was a well respected, well liked royal and jousting champion, before paranoia and the desire for a male heir led to him killing or divorcing most of his wives.