Key stats that tell you everything about SummerSlam 2018 and its Lesnar-Reigns main event

In Roman Reigns' WWE career, Brock Lesnar is the only person he's ever faced at least three times one-on-one without recording a single victory. ESPN

The 31st edition of WWE's SummerSlam pay-per-view -- the fourth-longest-running event in WWE history (behind WrestleMania, Survivor Series and Royal Rumble) is on Sunday. Since the inaugural SummerSlam in 1988, the pay-per-view has been held in 13 different states, as well as in Canada and England. This is the fourth straight year that SummerSlam will take place at the Barclays Center in Brooklyn, which followed six years in Los Angeles.

In what's almost certain to be the main event, Brock Lesnar will defend his Universal championship against Roman Reigns. With this being the fourth one-on-one match between them, and a title reign of this length in play, there are plenty of interesting stats in play. Get yourself up to speed heading into the match with the most consequences at WWE's second-biggest event of the year, followed by a quick look at the card's other featured bouts.

Universal Championship: Brock Lesnar (c) v. Roman Reigns

- On Sunday, Brock Lesnar will have been Universal champion for 504 days, the sixth-longest world title reign in WWE history and the longest of the last 30 years.

- The knock on Lesnar has been his lack of title defenses and television appearances throughout his Universal title reign. SummerSlam will be just his seventh televised title defense during his lengthy reign, and his first in 114 days (dating back to the Greatest Royal Rumble in late April). That is the longest span between title defenses for a WWE world champion since ... Lesnar's WWE championship reign in 2014-15 when he went 126 days between televised title matches.

- When Lesnar does show up, it is always on the big stage -- and he usually comes out victorious. Among the 46 superstars who have competed in at least 50 career WWE pay-per-view matches, no one has a better win percentage than Lesnar.

- If this match closes the show as expected, it would be the seventh time that Lesnar competes in the main event of SummerSlam -- passing John Cena for the most such matches in the 31-year history of the event. No superstar has won more SummerSlam main event matches than Lesnar (five).

- Lesnar was in the SummerSlam main event match in each of the previous four years -- the longest such streak in SummerSlam history. That means the Barclays Center has yet to see a SummerSlam main event that did not feature Lesnar -- and that doesn't appear likely to change in 2018.

SummerSlam main event matches since 2014

2017: Brock Lesnar (c) def. Roman Reigns, Braun Strowman and Samoa Joe
2016: Brock Lesnar def. Randy Orton
2015: The Undertaker def. Brock Lesnar
2014: Brock Lesnar def. John Cena (c)

- Roman Reigns will receive another world title opportunity on Sunday. SummerSlam will be Reigns' 14th world title shot at a pay-per-view event in the last five years -- four more than any other title challenger during that span. It's crucial to note that despite so many title opportunities, Reigns won just two of his previous 13 such matches.

- Reigns has taken on Lesnar one-on-one on three separate occasions, and failed to win any of those matches (includes Seth Rollins' Money in the Bank cash-in at WrestleMania 31). Lesnar is the only wrestler Reigns has faced one-on-one on at least three occasions without recording a victory.

- Could Money in the Bank potentially come into play again during a Lesnar-Reigns showdown? Braun Strowman currently possesses the Money in the Bank contract, guaranteeing him a Universal championship match at the time of his choosing. However, Strowman will be defending his contract in a match against Kevin Owens at SummerSlam, most likely prior to the Lesnar-Reigns title match.

- In the history of the Money in the Bank briefcase, the holder of the contract has cashed in at SummerSlam twice, and both came out victorious. Alberto Del Rio cashed in on CM Punk in 2011 to win the WWE championship, while Randy Orton cashed in on Daniel Bryan in 2013 (with an assist from Triple H) to become WWE champion.

Quick hits

- AJ Styles will defend the WWE championship against Samoa Joe. While SummerSlam will be the first time that Styles and Joe meet one-on-one inside a WWE ring, the two superstars actually competed against each other for world titles in other major wrestling promotions. In 2003, Samoa Joe successfully defended the Ring of Honor world championship against Styles. In 2010, Styles successfully defended his TNA world championship against Samoa Joe at Against All Odds.

- At SummerSlam, Styles will have been WWE champion for 285 days, the second-longest WWE championship reign of the last 10 years; CM Punk holds that record at 434 days from 2011 to 2013. Sunday will be Styles' ninth televised title defense during his current reign.

- Former UFC Women's bantamweight champion Ronda Rousey will challenge Alexa Bliss for the Raw women's championship. Rousey looks to join Lesnar and Ken Shamrock as the only athletes to win titles in both UFC and WWE.

- Carmella will defend the SmackDown women's championship against Charlotte Flair and Becky Lynch in the first women's triple threat match in SummerSlam history. If Flair wins, she will join Trish Stratus and Mickie James as the only six-time women's champions in WWE history.

- Dolph Ziggler will defend the Intercontinental championship against Seth Rollins. The Intercontinental title has changed hands 14 times at SummerSlam -- more than any other championship -- but not since 2014, when Ziggler defeated The Miz for the belt.

- Jeff Hardy will challenge Shinsuke Nakamura for the United States championship. Surprisingly, Hardy is 0-6 in his SummerSlam career, the worst record in the history of the event. Only John Cena has more SummerSlam losses (nine) than Hardy.

- Daniel Bryan will take on The Miz in a long-awaited match. Bryan is 3-1 all-time against The Miz in one-on-one bouts, including a win in their only previous pay-per-view meeting at Night of Champions in 2010, when he defeated The Miz for the United States championship. That was Bryan's first title victory in WWE.

- Braun Strowman will defend his Money in the Bank contract in a match against Kevin Owens. Only once in Money in the Bank history has a superstar lost his briefcase in a match. Mr. Kennedy won Money in the Bank at WrestleMania 23 in 2007 but lost his contract just over a month later in a match against Edge.

- The New Day are set to challenge The Bludgeon Brothers for the SmackDown tag team championships. The New Day look to become the sixth team in WWE history to win tag titles on five different occasions. Standing in their way, however is the fact that Harper and Rowan are a perfect 16-0 in standard two-on-two tag matches since re-debuting as the Bludgeon Brothers last November.