To get it out of the way: Fat Rob is not fat. The Redskins rookie running back is officially listed at 6 feet and 228 pounds, and you’ll find precisely none of the things you might expect from someone with his nickname — not the belly, not the jiggles, and not anything that would suggest he’s even remotely overweight.

In reality, Robert Kelley is mild-mannered and trim, with the NFL-ish quality of having no immediately apparent human vulnerabilities to things like freezing temperatures or gravity or the massive hurtling bodies of opposing defenders. He projects, like many professional football players, the distinct impression that he could pick you up and throw you a long way if he set his mind to it. He is large, basically, but not Large.

Kelley went undrafted out of Tulane, signed with the Redskins in May, and moved into the starting spot in Week 8 after a nagging knee injury sidelined Matt Jones. He has hung onto the job ever since, primarily on the strength of dazzling highlights like this:

“It’s kind of like you have to wait your turn being a free agent, and that’s what happened,” Kelley says of his meteoric rise up the depth chart on a recent afternoon at the Redskins’ practice facility in Ashburn, Virginia. “It worked out for me.”

Entering Saturday’s matchup against the Bears, the 7–6–1 Redskins are clinging to slim hopes of crashing the NFC playoffs. Kelley, a physical runner with a devastating cutback move, has emerged as a breakout star, rushing for 595 yards on an average of 4.3 yards per carry. Playing against the Packers on Sunday Night Football last month, he exploded onto the national scene, sparking a 42–24 win with 24 attempts, 137 yards, and three touchdowns in just his third career NFL start. His out-of-nowhere success has earned him comparisons to everyone from Alfred Morris, whose offseason departure for Dallas set the stage for Kelley’s ascent, to former Washington great Larry Brown.

And then there’s the nickname, a vestige of his college years. People love the nickname. The fact that Kelley is decidedly in shape has done little to dampen D.C. fans’ desire to root for a jolly avatar of carbohydrate consumption. “I mean, his nickname is Fat Rob!” The Washington Post’s Dan Steinberg wrote this month. “You can’t root against someone nicknamed Fat Rob.”

But the Fat Rob national audiences have come to know isn’t fat. So why has the nickname endured? And why is Kelley, who would have every reason to shirk a reminder of the darkest stretch of his football career, so readily embracing it?

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For as long as there have been athletes, there have been goofy athlete nicknames. And for as long as there have been goofy athlete nicknames, there have been nicknames that (a) didn’t make a lot of sense, (b) annoyed the hell out of the athletes assigned them, or (c) both. Consider Buccaneers running back Doug Martin, who has desperately attempted to supplant the sobriquet “Muscle Hamster” with “the Dougernaut.” Bills running back LeSean McCoy has beseeched fans to stop calling him “Shady;” former Celtics, Magic, and Clippers forward Glen “Big Baby” Davis would really appreciate if you called him “Uno Uno” instead. These players were all tagged with monikers at a young age, and for whatever reason they stuck.

But that’s the strange thing about Kelley’s nickname: It’s never really been his nickname until now. Despite the fact that it came from his position coach at Tulane, few knew him that way during his time on campus. “Some people called me Rob, some people called me Fat Rob. It wasn’t a big deal,” Kelley says. “If you go to New Orleans, you’ll hear maybe one or two people call me Fat Rob.”

Kelley was born in New Orleans and attended O. Perry Walker High School, on the west bank of Orleans Parish. He ran for 2,347 yards with 25 touchdowns during his prep career, and arrived at Tulane in 2011 as a three-star recruit according to Rivals.com. In his best season with the Green Wave — his junior campaign — he rushed for 420 yards on 98 attempts. Then, due to academic problems and a later arrest for simple battery and simple robbery (charges were ultimately dropped), he missed more than a year with the team, including all of the 2014 season, in which the starting running back job finally opened up following the graduation of Orleans Darkwa (now with the Giants) and seemed as though it might have been his.

Sitting in the stands of Yulman Stadium at the second home game of that fall, Kelley wept. When he returned to the team as a fifth-year senior in 2015, he failed to claim the starter job, instead sharing the role with a platoon of other backs, three of whom finished the year averaging more yards per carry than he did. He put on weight during his time away from football, coming in around 250 pounds. In one of his first practices back with the team, he threw up on the field.

Back home on the West Bank, people had wondered whether he’d ever make it back at all. “A lot of people doubted I was going to make it at place like Tulane,” he told The Advocate last year. “And then they were saying I’d never go back. That just pushed me harder to make them wrong.”

For Kelley, the “Fat Rob” nickname is a talisman of that era. It was the Green Wave’s then-running backs coach, David Johnson, who coined it, giving Kelley a backpack with “Fat Rob” stitched onto it as a joke. “Some people feel like I shouldn’t like the name, but it just reminds me that I was 250,” Kelley says. “I worked hard to get where I am.”

Kelley eventually lost the weight: He was down to 225 pounds in time for Tulane’s pro day in March, and when he graduated from college he became the first in his family to do so. His 40-yard dash at pro day was reportedly clocked at 4.68 seconds — not fast, but enough to make him call Johnson and gush. “He said, ‘Coach, coach, I ran a good time and I kept running the ball hard,’” Johnson remembered in an interview with The Washington Post. “He was so proud of himself and I was proud of him. It was really tough for him. Eighty or 90 percent of people would’ve quit if they were in his position.”

Those who know him aren’t surprised that his performance has drastically improved since. “It’s funny,” says Lazedrick Thompson, a senior running back for Tulane and a former teammate of Kelley’s, of the nickname catching on now. “He used to be the biggest one out of all of us.”

At training camp in Richmond, Virginia, this summer, it was quarterback Kirk Cousins who discovered the nickname, still emblazoned on Kelley’s bag. (Kelley calls it his booksack, an enduring bit of Louisiana terminology.) From there, it spread, eventually reaching head coach Jay Gruden, who referenced it during an August press conference. “‘Fat Rob,’ that’s what is on his backpack,” Gruden said. “That’s his nickname in college if you didn’t know that — ‘Fat Rob’ Kelley.” Once Washington fans at large caught wind of it — and watched Kelley shake off defenders and charge down the field — his identity was sealed.

“Here, that’s my name,” says Kelley, gesturing around the Redskins’ facility. “They don’t call me by my real name anymore.”

For the most part, Kelley has been apathetic about the persistence of the nickname. “I don’t really care, I’m just happy [doing] what I’m doing. They can call me whatever they want,” Kelley told reporters last month. Other times, he’s been less ambivalent: “I don’t like to talk about it,” he said in August. In recent weeks, however, he has started to embrace the name. He used it in his recorded player introduction before that Sunday Night Football appearance on NBC, and has taken to including it in tweets.

“I told him, hey, you need a marker there,” Johnson told The Washington Post. “Everyone has a brand.”

“We always knew Rob was special,” Thompson says. “He was always athletic, even though he was a bit overweight for his senior year. But we knew once he lost his weight — they finally started giving him the carries that he deserved, and the whole world could see how good he was.”

And the world has: Kelley opened the scoring for Washington in a recent 27–22 win over the Eagles, and logged the team’s only touchdown this week in an otherwise disheartening 26–15 loss to the Panthers on Monday Night Football. He’s bulldozed defenders and solidified his role in the Redskins offense, a development that has come as something of a shock, perhaps to no one so much as himself. “It’s OK for me to admit that I’m surprised,” he said in November. “It keeps me grounded.”

Kelley still has to remind himself of the sudden wealth and notoriety that come with being in the NFL: When asked about his favorite restaurant, he mentions the crab cakes at Oceana Grill in New Orleans, and says he goes there when he has the time and the money, before correcting himself: “Well, now I absolutely do.” (He’s on a three-year, $1.6 million deal that will keep him in Washington through 2018 — a small contract in NFL terms, but a whole lot by normal human and seafood-consumption standards.)

Still, he’s not exactly a household name just yet. Informed of the running back’s nickname on last Friday’s episode of The Rich Eisen Show, no less a source of Washington football pride than Matthew McConaughey asked, “What’s that about?” before endorsing it: “I already like it, though. I like it. I’ll look into that.”

Kelley’s acclimation to the NFL has happened in reverse: He established his persona before proving he can maintain his success. With the Redskins’ hopes partially riding on him now, though, he’s trying to figure the latter part out. “[This season] has been a lot of adapting to game speed, knowing where you fit in inside of the offense, knowing your role, playing your role,” he says. “It’s kind of been like trying to impress everybody.”