Unified WBA (Super), IBF, WBO and IBO heavyweight champion Anthony Joshua is set to defend his titles yet again on Saturday night as one of the biggest stars in the boxing universe is ready to make his long-awaited debut in the United States. Who does not come off as a big star, however, is Joshua's latest challenge: Andy Ruiz Jr., a Mexican-American heavyweight out of Imperial Valley, California. 

Originally slated to defend against Jarrell "Big Baby" Miller, Joshua and his Matchroom Boxing promotional team were left scrambling for a new opponent on short notice after Miller was removed for failing multiple drug tests, and that search culminated with the relative unknown Ruiz earning the biggest spotlight he's ever enjoyed in 10 years as a professional fighter. 

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The world of boxing at this point is very familiar with the English rockstar Joshua, so let's have a glimpse into some of the basics you need to know about the man who will be stepping into that Madison Square Garden ring on Saturday night looking to provide fans with a heavyweight shocker for the ages. 

1. Should Ruiz already have been a world champion?: Despite the unfamiliarity that exists among casual boxing fans, Ruiz's record is nothing to brush to the side at 32-1 with 21 knockouts. The one loss shouldn't be ignored, either. Ruiz challenged for a world championship previously in his career, battling Joseph Parker in December 2016 for the then-vacant WBO heavyweight title. Parker emerged as champion via majority decision, although many came away from that fight believing Ruiz had dominated enough of the early and championship rounds to earn the victory -- or, at the very least, a draw. In March 2018, Parker would lose the WBO title to Joshua via unanimous decision, so you could almost say that everything came full circle for Ruiz, only this time around he has more than just the WBO crown he can claim with a victory. 

2. Ruiz was the second choice for a Miller replacement: You could say that Ruiz is walking into the fight with Joshua this weekend feeling disrespected for more than one reason. While he may be miffed that fans are still wondering who he is in general, he wasn't the first option targeted to step in and face Joshua on short notice. Following the removal of Miller, promoter Eddie Hearn had his eyes on former WBC championship challenger Luis Ortiz to step in as Joshua's new foe. Hearn was so enamored with the thought of Ortiz -- who had put on a respectable performance against WBC champ Deontay Wilder in a March 2018 title fight -- that he reportedly offered Ortiz the largest payout of his career to play foil to Joshua on short notice. Ortiz and his team turned down the offer, however, with another potential big payday ahead for a rematch with Wilder. On the heels of a fifth-round TKO victory over German Alexander Dimitrenko on April 20, Ruiz then found himself in the right place at the right time, and quickly came to an agreement to challenge Joshua after he had specifically called for the fight following the win while explaining why it's an enticing matchup for him personally. 

"I think he's a perfect match for me," Ruiz said via ESPN. "Styles make fights. He's high, he doesn't have a lot of head movements, so I think with my speed and pressure, I think it would bother him a lot."

Funny how that worked out. 

3. Don't allow Ruiz's size nor his heritage fool you: Ruiz is a very captivating fighter for these two reasons. As a boxer of Mexican descent and someone whose physique makes it abundantly clear he's unable moonlight as a GQ model like Joshua can, it's easy for one to assume Ruiz is nothing more than a bruising brawler once the bell rings. That's not necessarily the case, though. 

While Mexican fighters are traditionally notorious for throwing caution to the wind in an effort to guarantee fans all-out slugfests, Ruiz values the sweet science a little more and brings with him above-average discipline. Particularly, Ruiz values his impeccable hand speed for someone with his frame, and his head movement isn't too shabby, either. A common premonition to this point among fans who have only studied Ruiz in a picture and searched his heritage was that he'll step in there on Saturday and wildly attempt to batter Joshua by scoring the killshot that would shake the boxing world to its core. It should actually turn out to be the exact opposite, though, as Ruiz will look to put his boxing skills to near-perfect usage for one night as he gets a second chance to make history and become the first-ever heavyweight champion of Mexican descent.