Before he became Samkon Gado, the insta-legend who was the talk of the Green Bay Packers for one sensational stretch of games, he was Samkon Gado, the unknown rookie called up from the practice squad. And so it was as the running back stepped onto an NFL field for the first time 12 years ago and took his position behind quarterback Brett Favre.

Gado was nervous. He was excited. He was, as he put it, "trying my best not to hyperventilate."

After all, he had started only two games in four years at Liberty University, had not been drafted and had not played a single snap in an NFL preseason game. Yet there he was, in an NFL backfield, facing 11 thundering behemoths, every single one of whom was much better than every single player he had ever faced. Gado couldn't help but wonder, "What am I doing here?"

Former Packers running back Samkon Gado is now an ear, nose and throat doctor doing a residency at Saint Louis University. He plans to return to Nigeria, his birthplace, to practice medicine in a few years. Saint Louis University

It's a question he has asked himself often in his life, from when he scored his first NFL touchdown to when he started medical school to the first time he put tubes in a child's ears as an ear, nose and throat surgeon.

On his NFL debut -- Oct. 30, 2005, at Paul Brown Stadium against the Cincinnati Bengals -- he caught a pitch from Favre and ran laterally. He says now that if that play had happened later in his career, he would have burst through the hole and scored a touchdown -- the hole was that big. But before he cut through the hole, he thought, "Wow, that's a big hole. I should run through it," and by the time he got done thinking that, it started to close. He still picked up 8 yards in his lone carry that day.

He started five of the next seven games and carried the ball 143 times that season for 582 yards and six touchdowns, including three 100-yard performances. He also caught 10 passes for 77 yards and one TD. His place in Packers lore went far beyond numbers on the stat sheet. He brought radiant sunshine to an otherwise dark 4-12 campaign, Green Bay's only sub-.500 season of the Favre era. He had a bright smile and powerful legs and a great name. Samkon means "truth" in Tangale (a language in his homeland of Nigeria) and represents his parents' belief in the truth of the gospel. He became an overnight hero in Green Bay, and that, he says, left him "absolutely terrified."

In his second NFL game in 2005, Gado carried 26 times for 62 yards against the Steelers and scored his first touchdown. A week later, he registered his first 100-yard game and added two more TDs. Jeff Hanisch/USA Today Sports

Gado, whose family moved from Nigeria to South Carolina when he was 9 years old so his dad could attend seminary, retreated to his furnished, two-bedroom apartment and lay face down, praying to God to help him keep his perspective intact. If he started to believe the great things people said about him, he might stop working hard, and if he stopped working hard, he'd stop being himself.

"I didn't want to be exposed as a fraud," he said. "I felt like I snuck in through the back door."

He knew that success for even the greatest football stars was fleeting. "The NFL is like a drug. When you're on it, it is a high high. But coming off that high is a bad crash," he said. "There had to be something else."

Even then, he knew what that "something else" was, and now he's on the brink of seizing it: moving back to Nigeria to put his skills as a surgeon to work.

HIS TIME IN Green Bay didn't last. Coach Mike Sherman was fired and replaced with Mike McCarthy. Gado's north-and-south style didn't fit McCarthy's offense, and after one game in 2006, he was traded to the Houston Texans. From 2006 to 2009, Gado played for the Texans, Miami Dolphins and St. Louis Rams, though he never managed another 100-yard day.

Gado quickly became a fan favorite in Green Bay, but, following a coaching change, the Packers traded him after one game in his second season. Allen Fredrickson/Reuters/Newscom

Gado credits his perseverance in the NFL and in his medical career in part to lessons he learned from Randy Geib, who did volunteer work training college and pro players in South Carolina. A youth pastor asked Geib to train Gado when Gado was still in high school. Geib, who wasn't really interested in working with somebody that young, reluctantly agreed and made the training ferociously difficult to try to get Gado to quit. That didn't work, and instead the two formed a bond that remains to this day.

"We just continued working harder and harder and harder," Geib said. "And he just kept getting better and better and better."

Carrying the ball from Nigeria Career rushing yards for Nigerian-born NFL players. Player Yards Seasons Christian Okoye 4,897 1987-92 Samkon Gado 972 2005-09 Adimchinobe Echemandu 110 2004-07 Patrick Egu 20 1989 *Nelson Agholor 14 2015-present Source: Pro Football Reference; * Plays wide receiver

In 2010, Gado went to camp with the Tennessee Titans but was cut. He waited the rest of the year to get picked up, but the phone didn't ring. He kept himself in shape just in case, and the New Orleans Saints finally called and said that if they won their opening-round playoff game against the Seattle Seahawks, they would bring him in for a tryout before their second playoff game.

Gado hoped his unlikely NFL journey would be restarted.

Then Beast Quake happened.

Marshawn Lynch's 67-yard, game-sealing touchdown run elicited a wild reaction from Seattle's fans that shook the ground enough to register on the Richter scale. The aftershock rumbled through Gado's life, too. He knew in that instant that his NFL career was over. Gado believes God had directed his path to that point (and continues to do so today). If it took a play such as the Beast Quake to snuff out his last chance at the NFL, well, Gado didn't need more convincing.

Gado began his studies at Medical University of South Carolina in 2011, two years after his final NFL appearance. Medical University of South Carolina

He was at peace with what he accomplished. He believed he had worked as hard as he could and gotten as much out of his talent as he could.

"Life is about winning the battle of attrition," he said. "It's not about the one who is the most talented. It's not about the one who is the most gifted. It's the one who chooses to say, 'I'm going to quit last.' If you're comfortable living in that space of absolute misery, that outlasts any kind of talent."

Football had never consumed him anyway. It was always a means to an end, and the end was returning to Nigeria as a doctor. He told his Liberty University head coach, Ken Karcher, about it during his recruitment and his wife about it on their first date. During NFL offseasons, Gado worked at nursing homes and hospices to enhance his medical school application. He tried to remain anonymous in doing so. He wanted an authentic experience, and if he signed up as Samkon Gado, NFL player, he wouldn't have gotten one. By concealing his "other" job, he got to change diapers and bed pans. "I wanted to truly get comfortable with that discomfort," he said.

He started at the Medical University of South Carolina in 2011 and graduated in 2015. For years, his sights had been set on a hard-to-get residency in the competitive field of otolaryngology -- ear, nose and throat -- at Saint Louis University. While in medical school, Gado reached out to Dr. Jastin Antisdel, the program director at SLU, for advice. Although Gado didn't have the best test scores, he impressed Antisdel with his humility and passion, and Antisdel invited him to do a month-long rotation in 2013.

"We put him through the wringer that month, asking him questions, making sure he was prepared, seeing if he had the wherewithal to do what it takes in what's a challenging career," Antisdel said. "He came through that with flying colors."

Gado graduated from Medical University of South Carolina in 2015, 10 years after he made his NFL debut. Medical University of South Carolina

By the end of the rotation, SLU ranked Gado No. 1 among applicants for two residencies. He has continued to grow as a doctor over the years, and his goals in Nigeria fit in well with the Catholic ethos of SLU: putting others first and taking care of people regardless of their ability to pay, Antisdel says.

TODAY, GADO IS in the third year of a five-year residency and is two-plus years away from moving back to Nigeria. That will be a leap even bigger than the one he made in football from high school to college and college to the NFL. To steel himself to make those jumps, he relied on a combination of his trust in God to guide him and his work ethic to prepare him. Now he is doing that again.

His friends believe he is uniquely prepared to handle whatever awaits him in Nigeria. "Sam has a strong sense of his Nigerian heritage. It runs deep through his veins, for sure. And so I'm not sure he really had a choice to stay and not go back," Geib said. "[He] meets challenges as well as anyone I've ever met, so I know wherever God lands him, he will make a huge difference."

Gado's humility and passion impressed Dr. Jastin Antisdel, left, the otolaryngology residency program director at Saint Louis University. Saint Louis University

Gado does not yet know where in Nigeria he will work. He grew up in a small town called Kufai, but he doesn't plan to return there. He will make an initial month-long trip to Nigeria in January. That will help him better understand how the health care system works and will allow him to see what ENT needs there are. He will bring his wife and three young sons, all under 4 years old, so they can get a look at the new world they'll be living in.

It's far more common for doctors in Nigeria to move to the United States (or Western Europe) than the other way around. There are more than 200 million people in Nigeria and only about 250 ear, nose and throat surgeons, Gado says. By comparison, a 2016 study found that there were 9,642 ENT surgeons in the U.S., which has 320 million residents. The lack of available treatment in Nigeria often means patients -- even the president of the country -- travel to India or Saudi Arabia for treatment, Gado says. Ear, nose and throat patients who stay in Nigeria are often treated by dentists, who have neither the proper training nor the expertise to handle complicated ENT cases.

With all those challenges, Gado knows it would be so much easier to stay in the United States. But he isn't going because it will be easy. He is going because he feels called to do so. Gado -- his last name means inheritance -- says he has an obligation to pay back what he has been given.

"I am standing on the shoulders of my grandfather and my father. I am reaping from fields that I did not sow," he says. "I take a look at all the things the Lord has allowed me to do, and I wonder, was it all for myself?"