The King of Chicago waltzes through the clubhouse, a just-used Oral-B jutting from one side of his 1,000-watt grin. Sammy Sosa stops to flex for a teammate and give a pound to a PR guy, finally gliding to a halt in front of his locker. He tilts his ear, doglike, toward the clubhouse speakers, which are playing alternative rock at dentist-office decibels. The King shakes his head disapprovingly.

Seconds later, Nelly is thumping from a boom box large enough to make RUN-DMC proud, a machine that Sosa keeps next to his locker explicitly for times like this, when pregame tunes get a little too Casey Kasem. The song is "#1" and Sosa's feeling it, nodding his head maniacally, like he's trying to shake water from one of his ears. Sammy belts out the chorus in his Dominican-accented English: "What does it take to be Number One?" He turns and beams. All eyes are on The King.

A few feet away, Mark Prior is in the training room, wrapping up a workout that began two hours earlier. He wears a sweat-soaked Army T-shirt and a look that could penetrate steel. When the music comes on, Prior pauses, rises and gently closes the door on the head-rattling bass lines. What does it take to be Number One? He's been in the bigs only for a month, but Prior already knows.

And his answer couldn't be more different from Sosa's. The slugger feeds off his lovable histrionics, which transform him from Samuel Sosa Peralta to Slammin' Sammy, darling of the North Side. But for Prior, the most heralded rookie in Cubs history, blocking out the distractions as well as the suffocating hype -- shutting that door and finishing your workout -- is what it takes to be Number One.

In a city that prefers its heroes larger than life, Prior is the anti-Sammy. He's focused, unassuming, all business -- 21 going on 40. Cubs fans may call him their savior, may hope he'll turn this cursed franchise around. But Prior tunes it out like he does Sosa's beats. He's the perfect man for this job.

***

It is May 22, 2002, and an electric anticipation is swirling in the Wrigley dusk, momentarily obscuring the reality that, at 15–28 and 11 games out, the Cubs have Wait 'Til Next Year written all over them. The gates open and fans rush in like they're on a game-show shopping spree. Only instead of running to outfield seats to snag Sosa's BP bombs, they elbow their way alongside the Cubs bullpen, where Prior is warming up for his debut.

Ever since their team drafted the USC player Baseball America touted as "possibly the best college pitcher ever," the citizens of Wrigleyville had been pining for this day. Prior finished his college career with an unreal season: 15–1, 1.69 ERA with 202 strikeouts and just 18 walks, a season Trojans coach Mike Gillespie could describe only as "bizarre." He struck out seven White Sox in three innings in March, prompting Sox skipper Jerry Manuel to call him the second-best pitcher (after Curt Schilling) he'd seen all spring. In a Triple-A pit stop in Des Moines, Iowa, Prior won his debut and crushed two solo homers; the PA blared the theme from The Natural when he came up in his next game. Even before Prior began his NASA-like rise through the minors, his Double-A West Tenn team called him before his arrival, offering anything he wanted (an extra locker, maybe?). They had him wear a handful of different hats during his stay, which they then eBay-ed for around $350 each. You might say people were high on this kid.

So by the time the second coming actually arrived, Chicago had worked itself into a lather. "Can't-Miss Kid," the Chicago Sun-Times dubbed him, running his picture above shots of Nolan, Roger and Randy. As Prior loosened up in the pen, fans stood along the third base railing, mere feet away, to have friends snap pictures like they were visiting the Statue of Liberty. Sosa's pregame jacks glanced off empty seats; everyone was busy getting a load of the next big thing.

And through it all, Prior's demeanor was as dynamic as a Matlock rerun. He never smiled, never looked up, except to flip his warmup ball into a sea of waiting hands. He then coolly fanned 10 Pirates, giving up two runs in six innings for the W. Afterward, teammates doused him with champagne. It was mere formality, a procedure, making official what everyone had known all along -- this was where Prior belonged.

He arrived only recently, but Prior's been headed for the bigs since MJ ruled this town. Ask Tom House. As a member of the Braves in 1974, House caught Hank Aaron's 715th home run in the leftfield bullpen. Now he's one of the game's premiere pitching instructors, and has another claim to fame: He's the man who molded Mark Prior.

	Only Prior can divert eyes from Slammin' Sammy.

House's company, Bio-Kinetics, has studied computerized analyses of Prior since he was a sophomore at University High in San Diego. House's jargon goes over the heads of most, but his take on Prior is crystal clear: "Logic says he could be among the best to ever throw a baseball." House has more than 300 big league pitchers cataloged in his digital files, and already Prior, 21, ranks fifth in the efficiency of his mechanics, behind Schilling, Johnson, Clemens and Ryan. Prior's fluid windup is hypnotizing, a unanimity of arms and legs spitting out disorienting changeups, knee-knocking curves and 95 mph fastballs on the black. House talks of Prior's surgical control and unflappable makeup; the ones who know Prior well all do. As good as he is, they've been expecting this from him for years.

The Yankees risked a supplemental pick on Prior (between the first and second rounds) when he was a high schooler in 1998. He didn't sign, not that anyone in Chicago would have noticed if he did. They were a little preoccupied with someone else at the time. Remember Kerry Wood?

But Mark Prior is no Kerry Wood. Sure, they both boast the sneaky-smooth fastball that shifts gears midway to the plate. And there was smothering buildup surrounding each man's debut. But Prior is far more polished than Wood was in '98. When he was drafted, Wood was striking out 17-year-olds still dizzy from that afternoon's physics exam. When Prior was picked, he was in the College World Series, staring down future first-rounders.

"He's been through it all already," says Wood. "He won't fall victim to any of the pressure."

On May 6, 1998, after Wood's legendary 20-K game against the Astros, the Chicago spotlight became a heat lamp. Accustomed to talking to the media only after starts, Wood suddenly faced constant questioning. "I felt more uncomfortable in the clubhouse than on the mound," he says, nodding at the glow of TV lights by Sosa's locker. "For three weeks, I went through what Sammy goes through every day." Pressure eventually dwindled to sub-Sammy levels, but Wood had elbow surgery and missed the next season. His coronation as the co-king of Cubbieland -- you know Sammy's not going anywhere -- was postponed. Three years later, Wood is 8–5 with a 4.12 ERA, second in the NL in walks and safely removed from the limelight.

Who's next in line to share the throne with Sosa? Joe Cesaretti, bartender at Cubby Bear, across from Wrigley on Clark and Addison, offers this anecdote: "These people came from Colorado and the first thing they asked was, 'When's Mark Prior pitching?' It was never this nuts when Wood came up." When Wood made history that May afternoon, it came out of nowhere. Prior's pedigree allows fans to expect greatness. "People believe in this kid," Joe says.

***

Most Mark Prior stories start from the ground up, or from the ankles up, because that's where Prior begins to be exceptional. He has the most monstrous calves you've ever seen, like dinner plates wedged into his stirrups. Prior's had them his whole life; he could reverse dunk a basketball in 10th grade. "Those things are bigger than my thighs," marvels catcher Todd Hundley. Prior's Double-A teammates nicknamed him Calfzilla. Those calves are the essence of his motion -- his fastball may leave from his right hand, but it starts in his calves.

As physically sound as Prior is, his first tour of duty with the hard-luck Cubs has been draining. As he sits in the dugout with his father, Jerry, and House on a rainy June morning, talk turns to his outing against the Reds the night before. Prior finished with a superb line (6 2/3 innings, two earned runs, five strikeouts) but a result (no-decision) that has become all too common. That's the rub when you play for the Cubs, who have the worst batting average in the NL (.241) and score just 4.2 runs per game. Prior's June 12 start against Houston was typical: 10 K's in six innings, leaving with a 4-2 lead. Juan Cruz then gave up three straight hits, leading to a bullpen-clearing circus and a 5-4 loss. That should help explain why Prior is the talk of the league, even though, through the All-Star break, he was just 2–2 with a 3.98 ERA. A little help and he's 5–1. His strikeout numbers (1.25 per inning) are off the charts, and on June 7 in Seattle, he shut out the mighty Mariners for seven innings and whiffed 11. (The Cubs won that one, 2-0.)

	There hasn't been this much buzz since Kerry What's-his-name?

"Some guys throw 95 and they're nice to hit off," says Reds third baseman Aaron Boone, another USC alum. "But he's got this easy windup and then -- whoosh! -- his fastball gets on you quick. He's the real deal." Against Prior, Boone struck out his first time up and was in a 1-2 hole the next. Then he guessed right on a curve and blasted one -- right at third baseman Bill Mueller to end the inning. Boone clubbed the plate, spiked his helmet and launched his batting gloves, along with a string of f-bombs, toward the dugout. He had reason to be mad: You guess right against Prior, you deserve a base knock.

Back in the dugout, Prior is still talking about the Reds game when Jerry's cell phone chirps. Mark freezes in midsentence. "Turn that off!" he hisses, glancing around. "We're not allowed to have cell phones out here." Jerry finishes his call and Mark relaxes. For now, he is all about not rocking the boat. "I've got eight major league starts," he says. "I know where I stand."

So do the Cubs. In spring training, Don Baylor, who was fired July 5, was pulling into his Mesa, Ariz., condo when a familiar voice came on the radio: "Hi, I'm Mark Prior." Baylor let the car idle. "Where do you think Mark Prior buys a Lexus?" It was a promo for the dealership where Prior had just scored his SUV. Baylor got a tape and summoned a team meeting the next day. "Guys, Mark Prior, the best college pitcher ever, has something to say," Baylor began.

On cue, Sosa (who else?) cranked his boom box, and the ad echoed through the clubhouse. Baylor let the grinning Prior go only when he promised to shuttle everyone around in his new ride.

Teammates constantly hunt for new material, but the ever-cautious Prior doesn't give them much. As Sosa says, screaming over his stereo, "He's always acting professionally. He knows he's our future."

Aside from grabbing some grub at Harry Caray's -- they told him to call anytime for a secluded table -- Prior doesn't go out much. He's still renting a room in a Lincoln Park brownstone from a relative. Eventually he'll look for an apartment. Not now. It's a distraction he doesn't need.

Let's be clear: Mark Prior is not a cyborg, Marinoviched since birth to be the perfect pitching specimen. He's funny, smart and down to earth, and his teammates know it. But as far as getting the word out to everyone else, well, Prior doesn't see how that will make him a better pitcher. In time, you'll see a different Mark Prior. Once he's had a few more starts, once his veteran teammates aren't waiting for that rare slipup, you might see the guy who wagers on everything from BP to long-toss with his fellow pitchers. Or the guy college roommates called Betty Crocker because of his kitchen acumen.

Or you might see this side of Prior: Last year at USC, against nemesis Stanford, some of the Cardinal players started mouthing off from the bench. Prior struck out the batter he was facing and told the guy, in no uncertain terms, to get the hell back in the dugout. He then turned to the on-deck circle and motioned the next hitter toward the plate: Get in there, son. It's your turn.

Imagine if he pulled that now ... the Wrigley crowd would go bananas. But don't hold your breath: "I popped off a lot in college but I doubt it's gonna happen here."

At least not this year. But when he earns his stripes, maybe Prior will start talking a little junk to get an extra edge. He's not ruling anything out.

He'll do whatever it takes to be Number One.

This article appears in the July 22 issue of ESPN The Magazine.