The cliche of the hero turned villain is one of the most despised tropes in comic book fandom and has resulted in some of the most loathed storylines in comics:

Emerald Twilight (Hal Jordan
Avengers Disassembled (Scarlet Witch)
Heroes in Crisis (Wally West)
Planet X (Xorn)
Cassandra Cain turns evil
Countdown to Infinite Crisis (Maxwell Lord)
Infinite Crisis (Superboy Prime and Alexander Luthor)
Countdown (Mary Marvel)

What are some examples of beloved heroes turning into villains on their own accord that were well recieved by fans?