DAVIE, Fla. -- Miami Dolphins running back Frank Gore returns to Indianapolis on Sunday (4:25 p.m. ET, CBS) the same way he left, as the NFL's oldest running back wiggling through tiny holes, wowing teammates and coaches and defying the odds.

That's exactly how Jim Harbaugh remembers Gore. One memory stands out: In 2011, Harbaugh's first season as 49ers coach, Gore was considered unlikely to play in an early October game at Philadelphia because of an ankle injury suffered the week before.

"I thought there was no chance he would play. His ankle was jacked up. It didn't make sense for him to go," said Harbaugh, who coached Gore from 2011 to 2014 in San Francisco.

But Gore convinced the 49ers to let him do a pregame workout, and he then convinced them to let him play. He ended up running for 127 yards on 15 carries, including the 12-yard winning touchdown with three minutes left. Then he converted two first downs on the final drive to ice a 24-23 victory over the Eagles.

"I was in awe," said Harbaugh, now back in the college ranks as coach of No. 4 Michigan. "I couldn't believe it. I never doubted Frank again after that."

Gore smiled and nodded recalling that game: "That was a good day. I'm a fighter. That's what I do."

Now 35, Gore continues to set records as the Dolphins' lead running back. In September, he passed Curtis Martin to become the NFL's fourth-leading rusher. Two weeks ago, Gore passed Walter Payton and Emmitt Smith for the most consecutive seasons (14) with 500-plus rushing yards. Gore has done it in every year of his career, and he has nine seasons of at least 1,000 rushing yards.

"I have no other favorite player ahead of Frank Gore," Harbaugh said. "There's nobody I respect more than Frank Gore. He's absolutely incredible."

ESPN talked with many of Gore's admirers in an attempt to figure out what makes the player known as "The Inconvenient Truth" so special.

What has allowed Gore to defy his age?

Gore hasn't missed a game since 2010. He also has overcome two torn ACLs, two shoulder surgeries, a fractured hip, a broken hand and countless other injuries. Gore is the first running back 33 or older to rush for 1,000 yards in more than 30 years.

Harbaugh: "Every player in the league is hungry. But most guys are hungry like they missed breakfast, but it's OK because they know lunch is coming. Frank is starving. He plays like he's never going to eat again."

Dolphins coach Adam Gase: "He enjoys first, playing, just in general. He loves everything from the time he gets in the building to practice. He enjoys all the little things that some guys -- they don't understand how valuable it is when you're young. ... It's almost like you forget where he's at in his career and he treats it like he's an undrafted free agent almost. He practices extremely hard. He finishes everything he does. There's a lot of pride there as far as what he does during a practice. Seeing him 10 years ago and then seeing him now, there's just not a lot of differences in how he plays and what he can do."

Dolphins RT Ja'Wuan James, recounting an interaction he had with Gore earlier this year: "I told him, 'I can't imagine what it was like 10 years ago blocking for you if it's like this now.' He maximizes runs, he sets up blocks and he knows exactly where to go. This is what it feels like to block for a Hall of Fame back."

What moments stand out?

For Gore, returning home to Miami has been a dream come true. He still lights up when Dolphins fans yell "The U" after a big run, which references his University of Miami roots.

Titans TE Delanie Walker (played with Gore in San Francisco from 2006 through 2012): "The Super Bowl [XLVII in February 2013], when he scored his last touchdown. We talked about that play in practice. I was his lead blocker. It was a counter play where I went one way and came back the other way. In practice, there was a defender there. He pulled me aside and said, 'In the game, cut that dude and I'll get in the end zone.' They called the play and he just looked at me. I knew exactly what he meant. The play worked out perfectly, just how he said it would. I cut Ed Reed, and he walked right in. He jumped up, pointed at me and yelled, 'Didn't I tell you!' He wasn't even excited about the TD. He was excited about the play turning out like he predicted and me making the block. You remember those little things."

Colts QB Andrew Luck (played with Gore in 2015-16): "Frank was the best type of teammate that you could ask for. ... He's just one of those personalities and one of those guys that you miss when he’s not around. I'm sure everybody in this locker room that has played with him at some point probably says, 'Yeah, I miss being around Frank Gore every day.' He's got an infectious personality. He's a heck of a football player."

Dolphins offensive coordinator Dowell Loggains: "The moments come in practice. They come in training camp. He has 'The U' magic from back in the day. That competitive grit, that toughness, that mindset he has. He has an old-school football mentality."

What is Gore's best attribute?

Gore's study habits have yielded an immense knowledge of his position. He has a detailed scouting report for every lead running back and many backups in the NFL. He might want to get involved with scouting or in a front-office capacity when he's done playing -- he's year-to-year and hasn't ruled out returning for 2019 -- but he has an endless bag of skills.

Dolphins running backs coach Eric Studesville: "His toughness -- mentally and physically. There's a unique toughness to say, 'I'm going to win, I'm going to outwork everybody.' He has some sort of internal disconnect button that says he's going to do whatever he can do to play on Sunday no matter what is ailing him."

Harbaugh: "He's one of the most incredible pass-protectors I've ever been around. He really understands third down and understands exotic blitzes. I also played with Marshall Faulk and they are both incredible at getting low and getting skinny."

Colts RB Marlon Mack (played with Gore in Indianapolis in 2017): "Frank has so many injuries that people don't know about. He's a fighter. He always goes out there and does his thing. You never know he was hurt. He always competes. That's the type of guy he is."

What have you learned from Gore?

One of Gore's most underrated qualities is being a mentor for young running backs. He has done it for Kendall Hunter and Carlos Hyde in San Francisco, Mack in Indianapolis, and now Kenyan Drake and Kalen Ballage in Miami. Gore picked up Drake after an overtime fumble at Chicago earlier this season that could have cost the Dolphins a game. He also shows love to former teammates Luck and Mack for their success in Indy.

Washington RB Adrian Peterson: "He's consistent and productive at an age where the NFL says you're over the hill. It's inspiring. He has always been a guy that I've been connected to and I've always followed. It's a mindset -- taking care of your body and being blessed with talent. I look at it like Frank Gore is still doing his thing at 35? Wow. I'm 33, why not me? He's definitely one of the guys that motivate me."

Ballage: "I've learned patience from him. A lot of patience. On the field, off the field, trusting the plan that God has for you. Watching him, and how he leads by example, is special."

Mack: "He taught me to just go out there and compete, no matter how bad things got last year. Let's go out there, do our job, work and help this team getting a 'W.' He’s always a phone call or text message away. I love talking to him. He's a great guy."

Drake: "He's been very beneficial for me. Every time I come in, I think I'm here early and he's always in here before me, early in the morning, getting extra work in. He has a full sweat going, like he's already did two or three practices."

Do you think Gore is a Hall of Famer?

Of the top 12 all-time NFL rushing leaders, all of those who are eligible are in the Hall of Fame. Peterson is ninth and widely considered a future Hall of Famer. Gore is fourth, 716 yards shy of passing Barry Sanders for third.

Walker: "He's probably the third-best all-time back in NFL history. If he doesn't get to the Hall of Fame, that's obviously politics. My dude don't talk, do a lot media or be in the limelight. If you're not dancing or show face, they put you on the back burner. That's the sad part of this league, that we don't recognize greats for being greats. Frank is a great. He's a true animal."

Studesville: "It's a no-brainer to me. The thing that makes him a Hall of Fame back is the consistency. From San Fran to Indianapolis to here, where he's had to split time. That's hard. He never had to do that before. But he hasn't raised his eyebrow one day. He just works every day. He's one of the most consistent backs I've ever been around."

Harbaugh: "He's one of the best to ever play this game."

ESPN NFL Nation reporters Mike Wells and John Keim contributed to this report.