(CNN) -- Many boxers have aspired to be the next Julio Cesar Chavez, but only one man was born to be.
His dad is an icon, a tiny man who cast a huge shadow. A man who lifted the entire nation of Mexico with his hands.
And despite his 46 victories without a defeat, Julio Cesar Chavez Jr. still has to answer the questions about his famous father, still has to punch through the skepticism, still has to face opponents who he says underestimate him because just they don't think he's as good as his dad.
"I can't help that people say that stuff about me. I am the son, and that is who I am," the 26-year-old said last week. "He is my dad, but little by little, I have proven myself. I have proven it in the ring."
The man he fights Saturday night in Las Vegas is another doubter. But he's more than that: He's terribly angry that his title was taken away and that of all people, the younger Chavez was the one who got it.
Sergio Martinez thinks it is a joke that Chavez is the WBC middleweight champion. He doesn't believe that Chavez has the skills. It was his name that won him a belt.
"The only reason he is world champion is because he is Julio Cesar Chavez Jr., the son of the legend," said Martinez, who is 49-2-2 and considered the third best fighter in the world, regardless of weight division.
Where Chavez is bigger and has often employed a simple, direct fight plan, Martinez moves quickly, is a cerebral boxer who thoroughly studies his opponent. Even at age 37, he will wear a foe down with superior conditioning.
"Martinez is a matador of the highest order, and Chavez is a bull of the highest order," Lampley said.
One thing that helps Chavez, Lampley said, is that he has a great chin -- that is, the ability to take a strong punch to the head -- like his father.
Unlike his father, though, Chavez didn't grow up poor. Boxing wasn't a way out and a way up. It was a way to impress his father, whom Chavez calls his idol.
Junior was always around boxing. He'd go to his father's workouts, even when he was very young.
Julio Cesar Chavez Sr. won his first 87 fights, taking titles in three weight divisions. He ended his career with a record of 107-6-2, including 15 victories over men who were or would become champions.
ESPN ranked him as the 24th best boxer of all time, and the Ring said in 2002 that he was among the top 20 fighters during the magazine's 80 years of publication.
But to young Julio, he was also a drunk and drug addict who was often hard to live with while growing up. It was the son who took the boxing legend to rehab.
The struggling father disowned his son but later thanked him.
"I would have died," the elder Chavez told HBO for the documentary series "24/7." (HBO, like CNN, is owned by Time Warner.)
Today, the father is a businessman with restaurants and car dealerships and an energy drink. But as his son's fight with Martinez approaches, the legendary fighter is a very interested observer and anxious teacher.
One evening, as night owl Julio Jr. emerges from his slumber, the father tries to give the begrudging student a lesson on how to box Martinez, who will seek to constantly move just outside Chavez's reach. The son looks disinterested and then jumps into the pool as his father continues to shadowbox and shout advice.
Later, the son sets up a spontaneous training session at the rental house where he is staying before the fight instead of going to the gym.
It's nights like this that anger his trainer, himself a legend in boxing for having coached more than 30 world champions. But none of them keeps a schedule like Chavez, Freddie Roach said.
The boxer trains where he wants to. At the gym, at the house, even outside at a cookout. He sleeps through most hours of daylight and then gets up and figures out whether he is going to meet Roach for a workout. Sometimes, he doesn't even go to the gym until 2 a.m.
Sometimes, he doesn't go at all, calling Roach, who has waited hours, and telling him his body isn't up to it today.
It frustrates the coach, who also trains Manny Pacquiao, among others. But he tolerates it.
"It's OK, as long as we get the work done," he said.
Lampley, who will call Saturday's fight, said Chavez has improved greatly since inviting Roach into his corner.
"He has a far greater sense of where to be and when to be somewhere in the ring," Lampley said. "He moves with much greater fluidity. He can set things up. He used to just walk in and fire punches. Now he does more to set up his punches, particularly the left hook to the body."
Just like his old man.
Roach admitted he's had work to do with the young prospect.
"He has the instincts of a fighter; he's just not a natural fighter like his father was," Roach said.
It is certain that Martinez, who came to the sport very late at age 20, doesn't think Chavez is the fighter his father was.
During a dual interview with boxing analyst Max Kellerman, Martinez glared at Chavez and said, "You're living in a delusion, based on your legendary father. When are you going to stop believing that?"
To which Chavez retorted, "I will never stop being my father's son."
But for Chavez to stop being just a son of legend and start on the path to becoming a legend himself, he'll have to beat Martinez on Saturday.