While tracking down the Joker in Switzerland, Jason Todd separated from Batman, ending up at an abandoned warehouse where he was captured by the Joker. The Joker proceeded to brutally beat Jason close to death. Having scattered explosives around the warehouse, Joker leaves Jason to die in the explosion

After some years, Jason return back but as a...Vigilante; He was more brutal and violent when it comes to crime fighting until then citizens sees him more of a 'villain' because of his actions that were supposed to mirror Batman himself. Jason, himself, doesn't even like Batman because of him being too lenient towards criminals since Batman didn't want to take their lives which resulting confrontations and conflicts

Neither way, he still has a good heart for protecting others especially children since they are young.