Harley Quinn

Harley Quinn is a criminal psychologist who obsesses over psycho killers, particularly the Joker, and follows his exploits with enthusiasm, like an obsessive stalker. She has come back from her accident and now goes by the name of Quinn as part of the Suicide Squad, an offshoot of the Justice League. She’s a little more dangerous than the Joker, but ultimately not much. Her motivations are less important than those of the Joker and Batman. Though she’s not a maniac, it’s not hard to imagine her sliding into the “fixer” role for the Joker, so he can focus on his more dangerous adventures.
At first, Harley is more of a side character, but she gains more prominence during Suicide Squad. Her “sweet” demeanor of being willing to cooperate with those she trusts makes her a good partner, even if she doesn’t quite get the most important job of listening to the Joker (by throwing more people into the jail instead of by focusing on the threat). She’s one of the only ones of the group that appears to truly enjoy herself in the jail. Harley’s work for the Suicide Squad is quite serious, with one segment of the comic detailing how she seeks to understand why the Joker is the way he is and whether he’s insane. A dream sequence implies that he might not be, but Harley’s internal monologue suggests that he may just be “an evil version of a kid that didn’t get the love he needed.” Harley holds out hope that she and the Joker can be friends, until she learns the truth about Joker and decides that he’s a sociopath. The first Joker appearances were more Joker-centric, but now that Joker is in the spotlight, the story has become more about Harley and her motivations for finding him.
Quinn and Harley are both fun to look at, and that’s what matters most. Harley is the scariest version of Batman that we’ve seen in the modern age. Quinn is goofy and scary in the same package. It’s hard to imagine the Joker ever being a cute, cuddly character, but Harley has taken it a step further.
We’ll have to see if she can go full Joker when she comes back from the dead, but in the meantime, we can use them both.