This past year was a bittersweet one for WWE as the leader in sports-entertainment made history with its women's division and dealt with one of its top superstars taking a leave of absence due to cancer.

Here are the Top 5 biggest moments that shocked audiences, changed the landscape of professional wrestling and rocked WWE to its core.

5. Raw celebrates its 25th anniversary

WWE celebrated 25 years of Raw being on the air in style in January with a special star-studded show that featured the return of wrestling legends.

Chairman and CEO Vince McMahon made a rare appearance and was honored with a plaque to commemorate the anniversary before he came face-to-face with his old nemesis Stone Cold Steve Austin. The Texas Rattlesnake delivered a crowd-pleasing moment when Austin nailed McMahon and his son Shane with a Stone Cold Stunner.

The anniversary show also partly took place inside the Manhattan Center where the first Raw was held in 1993 and featured legends such as The Undertaker, Christian, The Dudley Boyz, Scott Hall and D-Generation X consisting of Triple H, Shawn Michaels, Road Dogg, Billy Gunn and X-Pac.

4. Ronda Rousey makes her WWE debut

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Former UFC Women's Bantamweight Champion Ronda Rousey joined the WWE in 2018 and had her debut match at WrestleMania 34 in April.

Rousey, despite being new to WWE and having her first match at the biggest event of the year, performed admirably while teaming up with Kurt Angle to take on authority figures Stephanie McMahon and Triple H.

The tag team bout stole the show and had fans on their feet as Rousey turned Triple H into a punching bag and made Stephanie tap out to the Armbar. Rousey became a WWE star after just one match and used the momentum from WrestleMania to become Raw Women's Champion, a title she still holds.

Rousey dominated WWE like no other in 2018, defeating the likes of Nia Jax, Alexa Bliss and Nikki Bella, among others. As the Baddest Woman on the Planet heads into 2019, she is only getting started.

3. Daniel Bryan is medically cleared, returns to in-ring action

Daniel Bryan, who had announced his retirement from in-ring competition in February 2016, stunned the sports-entertainment world when he announced in March that he had been medically cleared to wrestle once again.

"I decided to fight. Fight for your dreams. And if you fight for your dreams, your dreams will fight for you," Bryan said at the time of how he never gave up hope about returning.

Bryan, one of the most popular superstars in WWE, came back with a vengeance by taking part in matches full-time on Smackdown. The return has been a dream for fans as Bryan's in-ring career was thought to be finished following multiple injuries.

Bryan's return year -- which included a feud with his longtime rival The Miz -- was capped off by Bryan becoming the WWE Champion in November after he defeated AJ Styles by cheating. He has since developed a new, meaner personality and has begun to attack fans for harming the environment.

2. First-ever all-women pay-per-view event Evolution takes place

WWE's women's revolution evolved in 2018 with the introduction of the company's first-ever female-only event, Evolution.

Evolution, which took place in October, featured two main events including Rousey vs. Bella and Becky Lynch taking on Charlotte Flair in a Last Woman Standing Match.

A Battle Royal that took place featured a number of female wrestling legends such as Michelle McCool, Alundra Blayze, Kelly Kelly, Molly Holly, Ivory and Torrie Wilson alongside current stars such as Asuka, Tamina, Zelina Vega, Carmella, Naomi and Nia Jax, among others.

The event was a celebration of the women's division and followed a number of other historical firsts such as the first-ever Women's Royal Rumble match in January and the first-ever Women's Elimination Chamber match in February.

Evolution was also where Lynch continued to become one of the biggest stars in WWE. Lynch, who also goes by The Man, has captured the attention of the WWE audience with her work-effort and quotable put-downs against other competitors. She is poised to take on Rousey in 2019 in what promises to be an epic confrontation.

1. Roman Reigns announces he has leukemia, takes leave of absence

The biggest WWE moment of 2018 is also the most heartbreaking. Roman Reigns -- who was the Universal Champion at the time -- suddenly and without warning announced on Raw in October that he has leukemia and would be taking a leave of absence.

Reigns was forced to relinquish his Universal Championship which he had finally taken from the clutches of Brock Lesnar following a long-fought rivalry.

The Big Dog delivered an emotional speech filled with thank you chants from fans and said he's had leukemia for 11 years.

"I wanna make one thing clear. By no means is this a retirement speech," Reigns said at the time. "I will beat this and I will be back so you will see me very very soon."

Reigns, who has main evented multiple WrestleMania's and had become WWE's poster boy, ended his announcement by embracing his Shield brothers Dean Ambrose and Seth Rollins. The trio gave each other their signature Shield fist-bump during a memorable moment that WWE will replay for years to come.

Reigns, should he be able to return to in-ring action, will surely take over the WWE once again. In any case, he left a mark on the company and on professional wrestling that will be felt forever.