That collective sound reverberating through the USC fan base Tuesday morning was a shared sigh of relief as the Trojans' quarterback musical chairs routine ended with one of the most touted QBs in the country taking his seat in Los Angeles.

This always seemed like the expected outcome ...

Caleb Williams, the No. 1 dual-threat QB and No. 6 overall national prospect in the 2021 recruiting class, out of Gonzaga High School in Washington, D.C., went to Oklahoma to play for Lincoln Riley. Riley left after the season for USC. Williams entered the NCAA transfer portal after the Sooners' bowl game. Williams visited Los Angeles, posting on Instagram from Rams and Lakers games. Projected Trojans starting QB Jaxson Dart entered the portal last month and landed at Ole Miss.

All the signs were there, and yet when the announcement wasn't immediate, as Dart found a new home at Ole Miss while USC still didn't officially have a quarterback, some degree of panic set in on social media and message boards.

But all was made right Tuesday as Williams posted his announcement -- he's a Trojan.

Not just a Trojan but the new face of the program along with Riley.

So why all the hype for the rising sophomore? Allow us to explain who Caleb Williams is and how he got here ...

RELATED: QB Caleb Williams makes it official -- he's a Trojan | Adam Gorney's scouting report on new USC QB Caleb Williams

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Sports Illustrated's Ross Dellenger wrote an in-depth feature on Williams earlier this fall when he took over the starting job at Oklahoma. It explained the origin of the 'Superman' nickname that was attached to the star QB during his time at Gonzaga HS in Washington, D.C.

The moniker may have preceded it, but one defining game and play really brought it to life.

As Dellenger wrote:

On the final pass of his sophomore season in 2018, Williams completed a 53-yard Hail Mary to earn his team a championship. “That’s part of his legend here,” says Randy Trivers, Williams’s head coach at Gonzaga, an all-boys Catholic school in the nation’s capital.

Gonzaga had fallen behind 20-0 to local powerhouse DeMatha in the Washington Catholic Athletic Conference championship game that year before a wild finish that saw three touchdowns scored in the final 29 seconds -- the last of those, with Gonzaga trailing, was the Hail Mary from Williams to win it.

From Dellenger:

The play is immortalized in such a way on campus that it is used as a greeting. At the start of an interview this week, athletic director Joe Reyda leans across his desk and, in a hushed tone, says, “So you know about the Hail Mary, right?”

Speaking of comebacks, Williams furthered his legend in the Red River rivalry game vs. Texas, coming off the bench for Oklahoma, replacing starter and former five-star prospect Spencer Rattler, and added yet another momentous comeback to his growing legend.

Oklahoma trailed 28-7 when Williams was inserted in the game at the start of the second quarter and ran for a 66-yard touchdown on his first play, on fourth-and-1.

Williams finished that Oct. 9 game 16-of-25 passing for 212 yards, 2 TDs, 0 INTs and 88 rushing yards. His 52-yard touchdown pass to Marvin Mims midway through the fourth quarter tied the game at 41-41 before Oklahoma ultimately won 55-48 in the final seconds.

From Dellenger's SI feature:

His dad, Carl Williams, opened a sports training and recuperation facility in Maryland called Athletic Republic, the first step in sculpting his son’s body into what we see today—a big, fast, powerful specimen that reminds some of Dak Prescott and others of Patrick Mahomes. Mahomes, though, isn’t as thick, nor is he as quick as Caleb, says Schaechter, without a hint of sarcasm.

As a high schooler, Caleb had a support team that would rival many NFL passers. He not only had access to the family-owned training facility, but also had a strength and conditioning coach, multiple passing instructors and a dietitian, his father. When he began playing quarterback, Carl put his son on a diet to keep him fit to play the most important position on the field.

Rivals' Carey Murdock shared an anecdote about Carl Williams from the QB's recruitment at Oklahoma:

He once told Lincoln Riley if he didn’t offer his son a scholarship, he might show up anyway if they decided Oklahoma was the best place for his son to play college football.

“If we decide if this is the best place for him, this is where he’ll be. It won’t matter. And you’re going to have one hell of a competition on your hands,” laughed Carl Williams when thinking back to his first meeting with Riley. “That’s what it is right? I think (Riley) understood that. We approached it a little bit differently.”

Williams has 68.8K followers on Twitter and 112K on Instagram, making him one of the most marketable college football players in the Name, Image, Likeness era.

Former NFL QB Charlie Batch grabbed headlines earlier this month when he suggested there could be a $1 million NIL deal if he chose to play at Eastern Michigan.

On3.com recently ranked Williams' 14th on its NIL 100 list with an estimated valuation of $434,000.

He even appears to have his own logo created:

Williams was the No. 1 ranked dual-threat QB and No. 6 overall national prospect in the 2021 recruiting class, and Rivals national recruiting director Adam Gorney suggested that might not have been high enough based on the early returns.

While taking over the starting job in October, Williams completed 64.6 percent of his passes for 1,916 yards, 21 touchdowns and 4 interceptions and rushed for 442 yards and 6 TDs.

His biggest passing day statistically was against Texas Tech when he completed 23 of 30 passes for 402 yards, 6 TDs and 0 INTs. He completed at least 75 percent of his passes in four of his starts with the others being:

-18 of 23 (78.3 percent) for 295 yards, 4 TDs, 0 INTs, plus 66 yards and 1 TD rushing vs. TCU

-15 of 20 (75 percent) for 178 yards, 2 TDs, 1 INT, plus 70 yards and 1 TD rushing vs. Kansas

-21 of 27 (77.8 percent) for 242 yards, 3 TDs, 0 INT vs. Oregon in the Alamo Bowl

Overall, Williams had five games with at least 60 rushing yards, including 60 yards on 4 carries vs. Western Carolina before claiming the starting job.

"After seeing him at Oklahoma perform the way he did, probably not [rank him] high enough," Gorney said. "Just an incredible decision-maker. He has all the arm talent in the world, so that's not of question, but quarterback is so important when it comes to decision-making and where he puts the ball, and that has been proven to be at the elite level. ... He's a great decision-maker, he is definitely a dual-threat guy that can get out. I think we saw a lot of those runs during his time at Oklahoma and I think that should continue at USC. ...

"[He was] setting himself up to be in contention as the No. 1 QB drafted [in his class]. When Lincoln Riley leaves, I think that opened it up pretty clearly that he was also going to leave and follow him, and now is in the exact same situation. Can still be the No. 1 quarterback off the board, just from USC now."