While Batman stands for order and good in the world, the Joker is an agent of chaos. But there have been times when the Joker was good.
Yes, he frantically sows as much terror as possible as he attempts to prove that everyone is a monster on the inside. Where Batman demonstrates what people can be at their very best, the Joker is the exact opposite. He shows us what people can be when they lose their morality and instead act entirely on impulse.
All this hasn’t stopped the Joker from occasionally showing his human - and even virtuous - side, however. Whether it's a brief moment of realization of the things he's done, a complete shift in thinking that makes him a hero, or even a temporary partnership with Batman, good guy Joker does exist in the DC universe. You just have to dig deep into all of the plots to find him.
You might also be interested in this list of The Best Joker Storylines.
When He's Cured And Helps Gotham In ‘Batman: White Knight’
When He Lives A Normal Life In ‘Batman: Going Sane’
When He Accepts His Imprisonment In ‘The Dark Knight Returns’
When He Helps Defeat The Black Glove Group In ‘Batman R.I.P.’
When He And Batman Work Together In ‘Dark Nights: Metal’
When He Is A Hero Fighting Villains In ‘Countdown’