PITTSBURGH -- The Pittsburgh Steelers call him "Big Dan." They perceive the 6-foot-7, 352-pound Big Dan as giving questionable effort at times, and he's earned at least some of that perception. He is big-bodied potential unfulfilled after four seasons, re-signed on a minimal one-year deal for depth.

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His family calls him "Daniel Ray." Daniel Ray is sweet-natured. Behind a sad face is a shy, gentle man who wants to play football and video games and chill out. He wants to go hard every snap, but sometimes he gets tired.

Big Dan needs to be pushed and told repeatedly to get nasty. Daniel Ray isn't mad at his parents for bouncing in and out of his life. On and off the field, riling him is an arduous task.

But Dan McCullers is tired of watching teammates get rich, so he's bringing Big Dan and Daniel Ray together, hoping to find his edge on the field and get angry for good.

"They signed me back to a one-year deal -- well, I want a multiple-year deal," McCullers said. "I just have to work hard and grind my ass off so they can sign me for multiple years and I can make that money, set up my family to be good."

A motivated McCullers is exactly what the Steelers want. A former fifth-round pick with 28 career tackles in four seasons, he has earned some first-team reps in this week's practices after an active performance in the preseason opener in Philadelphia. And he impressed on Thursday against the Packers, starting the game and driving an interior lineman back and into the turf on two of the first three snaps.

Players and coaches are forecasting greatness -- with a qualifier.

"If that guy can get his motor running like we see it do sometimes, he can be a dominant force," defensive line coach Karl Dunbar said.

"Once it clicks for him, it's going to be dangerous," defensive tackle Tyson Alualu said.

At 6-foot-7, 352 pounds, Steelers defensive lineman Dan McCullers is still an intriguing prospect, even after four seasons in the NFL. George Gojkovich/Getty Images

The NFL's biggest defender has teased them before, surging into the backfield one play and getting moved by an undersized center the next. The Big Daniel Ray transition has McCullers viewing bigness no longer as unrealized potential or judgment but as a great way to make a living.

"We're really trying to figure that out for him, how to turn it on and off," said McCullers' older sister, Deonica Sanders, whom McCullers nicknamed "Nuk." "He's had to realize, '[Getting angry] is what I need to do for my job.'"

'Be the baddest dog in the pound'

Even after watching him for years, an approaching McCullers requires a double take. His fists are meat blocks, his calves spacious Miami real estate. His thick cheeks and well-manicured mustache resemble a chubby teenager turned mammoth man.

Size is a way of life for the McCullers family. McCullers was a 300-pounder by ninth grade. His grandfather Donnie, a funeral attendant who proudly raised him and his two sisters "under the blood of Jesus" outside Raleigh, North Carolina, was once 400-plus pounds. His mother is 6-foot-3.

Classmates constantly teased McCullers for his girth, and Sanders believed McCullers bottled that pain up until he got home. She has seen him punch a wall or two.

"I felt the teasing broke him in some ways," Sanders said. "Up until his senior year, he was almost childlike. We were sheltered and well-taken care of."

Dan McCullers with his mother Phyllis McCullers and father Marcus Sanders, who both bounced in and out of his life. Courtesy McCullers family

Still, Donnie would experiment with his grandson's anger. After noticing some laziness, Donnie told him, "You're too tall to be flipping hamburgers."

"I ain't flipping no hamburgers," McCullers snapped back.

"Then be the baddest dog in the pound," Donnie told him.

One kid who kept prodding McCullers once got the dog's wrath in the bathroom after class.

"Growing up as the big guy, bigger than everyone else, people try to test you and stuff -- you've got to show them to leave you alone," McCullers said.

McCullers didn't grow up playing football and failed to make his eighth-grade team, but once he secured a spot on the high school squad, he could always move a pile and command double-teams. Strength carried him through the junior college circuit, into the University of Tennessee's lineup and onto the Steelers roster, where flashes of practice brilliance are stuff of legend.

A few years back, McCullers moved back Pro Bowl center Maurkice Pouncey and tackled Le'Veon Bell in the backfield. Linebackers coach Joey Porter still references that play to McCullers. Do that every snap, he tells him.

And that's the problem.

"It's me -- mentally. I'm stopping myself," McCullers said.

The Steelers' Dan McCullers has teased with his potential on one play only to be pushed out of the way on the next. Kevin Hoffman/USA TODAY Sports

Raw talents get more chances

Defensive coordinator Keith Butler has three sons, and two of them absorb his advice. The youngest one doesn't listen to much of anything.

"I think [McCullers] is a little bit like the one you can't tell anything," Butler said. "Not that he's disrespectful, because he's not. But it's tough on him. He's still in the learning phase ... No matter how big they are, you don't know how mature they are mentally."

This raises a question: How long can an NFL project develop before it's too late. Those observing Steelers practices over the years watched then-defensive line coach John Mitchell decry McCullers' poor technique and bad leverage. McCullers was a permanent fixture on the bench during a contract year, playing 13 snaps along the line in 2017. The Steelers gave him a $90,000 signing bonus on a one-year deal. Bringing him back at all was considered a mild surprise.

But raw talents get more chances, and the hiring of Dunbar -- with Mitchell moving to assistant head coach -- symbolized a fresh start.

McCullers and Dunbar both know the core issues: effort and attitude, which McCullers at least partly attributes to conditioning and fatigue. Dunbar is getting what he needs in those areas, so he doesn't need to yell. And he wants to play two nose tackles, which bodes well for McCullers and third-year player Javon Hargrave.

"I think his effort and his attitude has changed, and you can see it in his performance in practice and especially in the game last week," Dunbar said.

"He's always been the one everyone thought wouldn't make it, so to prove not just to other people but himself that he can play at a high level for a long time, I'm so proud of him, because he did this all on his own." McCullers' sister, Deonica Sanders

McCullers chasing down the Eagles' third-string quarterback from the pocket to the sideline was a welcome sight for Steelers coaches seeking results and family members seeking urgency on and off the field. Oftentimes, McCullers still looks unfazed, almost polite in one-on-one drills.

"Trying to go out there every day to push yourself to get better, that's something I have to keep working on," McCullers said.

A transformation

The signs of stunted maturation surfaced earlier in McCullers' NFL career. He didn't get his driver's license until he was 22. He simply got rides everywhere. He just now started handling his own NFL money after Donnie did so for the first four years. He has an affinity for Cap'n Crunch cereal and video games.

Now, instead of saying "Grandpa, you handle it," McCullers recently told Donnie he wanted to invest his money.

The lack of guaranteed money available in free agency was humbling.

"I taught him to always strive to be the best in whatever you do, and I think that now he's ready to show his best," Donnie said. "Some children grow up faster than others. Some grow up slower than others. But he's a good guy."

Defensive line coach Karl Dunbar says Dan McCullers' "effort and his attitude has changed" and it's evident in practice and games. Jeremy Fowler/ESPN

And a well-portioned eater. He has stayed in the 352-pound range by dropping the Cap'n Crunch for lots of fish, water and salads. Big Dan realized cereal is bad for you unless you eat the healthy kind, and "I like the bad kind," he said.

Off the field, McCullers has helped bring his family together, inviting both parents to family day at training camp. Donnie believes his grandson will always carry the void left by his parents as a teen. One area of adulthood that McCullers always embraced was forgiveness.

"Nobody's perfect. They are getting better," McCullers said. "Just taking it day by day, trying to be the best they can be. Every family has problems -- you just have do work for it."

The perceptions will follow lazy Big Dan until he produces on the field. But Daniel Ray can't fail.

"This is really a transformation of a shy, young guy who stayed to himself to a man who's assertive and interested and wants more with his life," Sanders said. "He's always been the one everyone thought wouldn't make it, so to prove not just to other people but himself that he can play at a high level for a long time, I'm so proud of him, because he did this all on his own."