Suicide Squad was negatively received when it was first released largely due to Jared Leto's depiction of the Joker, but it might have been totally different if Ryan Gosling hadn't turned down the role. The 2016 comic book adaptation is part of the DCEU and introduced Harley Quinn and a new version of the Joker to moviegoers. It follows the titular team as they're recruited by Amanda Waller to stop Enchantress. In return for completing the mission, they would have a few years taken off their prison sentences.

https://screenrant.com/ryan-gosling-turned-down-joker-suicide-squad-reason/