SANTA CLARA, Calif. — The legend of Justin Smith began long before he shoved a Pro Bowl left tackle backward into his own quarterback, as if steering a child’s push toy, on national television. It began even before he chased down a wide receiver in the open field to cause a fumble earlier this season.

It only seems as if Smith has just arrived, along with the rest of the San Francisco 49ers, after years in the N.F.L. wilderness. The 49ers will take one of the best defenses into the N.F.C. championship game against the Giants on Sunday, and Smith is such an important part of it that he earned All-Pro honors at defensive tackle and defensive end — the first time a player has ever accomplished that — and is a leading contender to be the league’s defensive player of the year.

But if this season has finally been Smith’s coming-out party, one 11 seasons in the making — and if the game against the Saints was his star turn — then Smith first made an impression when he was still a high school senior, having just signed a letter of intent with Missouri. It was a fall day and the Tigers were practicing when Smith, already with a massive frame, began a long, slow walk to watch his new team.