Killers. Thieves. Gangbangers. Cannibals.

The new DC Comics film “Suicide Squad,” out Friday, is made up of some of the worst of the worst criminals, but writer/director David Ayer doesn’t think the ragtag group of villains-turned-heroes are all that bad.

“It’s a movie about people who have done bad things, and not necessarily about bad people,” he explains. “These guys aren’t evil, they’re totally redeemable and that becomes the big central thesis, in a way. ... When is there no hope for them? When can the heart no longer change? And these are guys who grow and they learn a lot and they form this family and they actually do something pretty wonderful.”

The Suicide Squad is made up of some familiar baddies from the DC Universe — both obscure and recognizable — including Deadshot (Will Smith), Harley Quinn (Margot Robbie) and Captain Boomerang (Jai Courtney).

The team is brought together by Machiavellian government agent Amanda Waller (Viola Davis) to handle the worst situations in a world with wondrous women and super men.

Ayer says he was “attracted to making a film about the bad guys,” and as he was figuring out the lineup for the team, he says one name seemed to be quintessential to the film.

“I just felt like I couldn’t do it without Harley Quinn,” he says. “I felt like the day had come for this character, to present her to the world. If you have Harley, you got to have Joker to understand her world and backstory. It was like curating a cocktail party, making sure you have the right mix of personalities.”

Quick background: Harley — created by Paul Dini and Bruce Timm in the mid-1990s in “Batman: The Animated Series” — is Dr. Harleen Quinzel, a psychiatrist at Arkham Asylum with a few screws loose, who becomes the girlfriend of the Joker (Jared Leto).

“Margot became really fascinating to watch because she just jumped off the cliff every time,” Ayer said. “She’d do different things on different takes and was fearless.”

And based on the scope of “Suicide Squad,” and the sheer number of characters and plot lines, Ayer had to be a bit fearless himself in taking on the film.

“I couldn’t have done this as a second or third movie, for sure,” he says. “It stretched every hard lesson that I’ve learned about storytelling and moviemaking, and then I learned a whole new set of lessons. It’s an insanely complex movie. It’s not a truly linear plot.

“There’s a lot of characters, a lot of characters to introduce, a lot of story mechanics,” Ayer continues. “Finding the balance — having all these pieces work together — that’s incredibly challenging. That’s probably like an air traffic controller at JFK.”

Working on a film this expansive was made easier with its impressive cast.

The director says newcomer Karen Fukuhara — who plays the mystical sword-wielding hero Katana who helps the Suicide Squad — really surprised him.

“She’s such a freshman in the industry and she really understood her angles and understood how to work the camera,” Ayer explains. “I don’t know if it’s instinctual or where all that came from, but she really brought a lot to the character.”

On the other end of the spectrum, Emmy-winner Davis brought a world of experience to Waller, a key figure in the film.

“It’s one of those roles that if not done right, could just be mechanical,” Ayer says. “She turned Amanda Waller into a real character, someone who really jumps off that screen. Someone who has to be every bit as strong and capable as the supervillains that she’s outfoxing.

“She’s unbelievable,” he continues. “She can read the phone book and you’d be thrilled to watch it.”