Take a look back at some of the most thrilling Royal Rumble moments from The Rock, Hulk Hogan, Stone Cold Steve Austin and more. (4:57)

Editor's note: This story was originally published ahead of the 2018 Royal Rumble.

The Royal Rumble is one of the most anticipated events of the year. It's easy to see why.

The stakes couldn't be higher. It's not just a WWE or Universal title shot -- it's a title shot at the biggest event of the year, WrestleMania. It's an opportunity to be in a marquee match at the "grandest stage of them all."

But that's not the only reason for the appeal. The fans enjoy the unpredictable nature of it. In theory, 30 wrestlers have a shot to seize the opportunity. In reality, booking dictates how many contenders realistically could win. It's often just a few, and often the winner seems inevitable (think Hulk Hogan in 1990-91 or Steve Austin in 1998 or 2001).

Just as stimulating as the actual winner are the surprises that take place along the way. When the buzzer goes off, WWE has proved that just about anybody can walk through the curtain and take their place in the match. The disbelief and shock value is just as big a part of this match than the actual action.

With the addition of a women's Royal Rumble in 2019, also with a full field of 30 (with just over half of those spots announced and not many members of the main roster not included), there are twice as many opportunities for jaw-dropping moments.

We can break down the surprise Royal Rumble entrants into a few categories.

The field-fillers

During the early 1990s, it could be a challenge getting to 30 entrants, let alone putting together a field with numerous potential winners.

So there was a series of entrants from outside the WWE (then WWF), or entrants who had been away from WWE for quite some time. There was legends from the wrestling world like Carlos Colon in 1993, Greg Valentine in 1994 and Dick Murdoch in 1995.

The 1996 Royal Rumble featured a series of entrants bordering from "who's that?" to "why him?" like the Squat Team, Takao Omori, Dory Funk Jr. and Doug Gilbert.

These took place during a lower point in the Royal Rumble time, as WWE struggled to put together a field of compelling entrants.

Mr. Perfect entered the 2002 Royal Rumble at No. 25. Courtesy WWE

The legends

The Attitude Era brought a myriad of changes to WWE. In terms of the Royal Rumble, it brought a feeling that anything could happen and anyone was a potential entrant.

It started in 1998, when the Honky Tonk Man entered 19th and lasted about 20 minutes before being eliminated by Vader. He hadn't wrestled a WWE match since 1990. HTM made another surprise appearance in 2001, in one of the most memorable spots in Rumble history. He interrupted Kane, who was in the midst of a breakout performance, to perform a musical number. He ended up with a guitar broken over his head and a quick elimination by the Big Red Machine.

The blast from the past is a regular part of the Royal Rumble. Although rarely does the surprise return make an impact of the result on the Rumble -- Mr. Perfect's final-three appearance in 2002 the exception -- it still gives a chance to revive memories while not exposing anyone who's not in ring shape.

Bob Backlund (2000), Haku (2001), Tatanka (2006), Jimmy Snuka (2008), Roddy Piper (2008), Hacksaw Jim Duggan (2009, 2012), The Godfather (2013), Diesel (2014), The Boogeyman (2015) and Diamond Dallas Page (2015) prove that the legend is a valued part of booking a Rumble.

Michael Cole even stepped into the ring during the 2012 Royal Rumble. WWE

The comedy spot

With the Rumble match lasting around an hour, some levity is needed at spots. The legend spot can provide some laughs, but there are some competitors whose inclusion in the Rumble is solely for laughs.

Drew Carey in 2001 was announced earlier in the night, but going into the night, it was only announced he'd be in attendance. He's the only true celebrity from outside the wrestling world to enter, but that doesn't mean that some non-regulars in the ring can't enter themselves.

You have announcers such as Jerry Lawler, Booker T, and, yes, even Michael Cole entering in 2012. Or personal ring announcers like Ricardo Rodriguez in 2012, who had one of the best entrances in Rumble history (WWE Network to do it justice). Women like Beth Phoenix and Kharma have surprised and had memorable eliminations, Phoenix taking out the Great Khali, Kharma eliminating Cole.

John Cena surprised the MSG crowd as he returned from injury to enter the 2008 Royal Rumble. Courtesy WWE

The surprise return

With dirt sheets and smart fans part of the wrestling landscapes in the current era, it's hard to make anything a true surprise. But occasionally, WWE can pull a fast one.

Occasionally, it's a wrestler returning to the roster full time, like Mr. Perfect in 2002 (who made it to the final three), Rob Van Dam in 2009 or Bubba Ray Dudley, whose 2015 Rumble appearance set up a full-time return not long after.

Bubba Ray Dudley on his Rumble Surprise If you go back and you watch the video, but more importantly listen to the audio of my surprise entrance in the '15 Royal Rumble, you can hear everything you need to here. You don't even have to watch, just listen. You heard how the WWE universe responded to me coming back. You heard how the WWE universe responded to me and D-Von coming back the night after SummerSlam at the Barclays Center. We've always had a great relationship with our fans and our fans have always loved us. People knew what we brought to the table. That response in Philadelphia shocked everybody backstage at WWE. Nobody expected that, but I expected nothing less. When you leave the WWE, the WWE doesn't expect you to be as successful as you could've been in WWE. Me and D-Von were gone for 10 years and Team 3D became as big of a name, if not a bigger name than the Dudley Boyz. The Dudley Boyz only existed in the WWE. Team 3D existed around the world within TNA,and within All-Japan, and New Japan, and every other promotion in-between that wasn't the WWE. So when I went back for the Rumble they're expected a fun little nostalgia pop. That's not the pop that I got. The pop that I got was genuine in that people were really, really excited to see me back. If you go back and watch, you actually hear the people chanting for D-Von about 10-15 seconds before I got eliminated. The WWE wanted the Dudley Boyz back.

But more often, it's an early return from injury, as time and again wrestlers prove their superhuman ability to recover from injuries.

The best two examples of this taking place came in 2008 and 2010, when John Cena and Edge made surprise returns from injuries, entered 29th or later, and ended up winning the Rumble. Sheamus, in 2014, made the final three when he wasn't yet expected back from injury at that time.

The debut

This is the category that both fuels the most speculation and excitement. With independent and international wrestling more accessible to viewers through new forms of media, debuting in the Rumble means that more fans already know who you are. No need for weeks of promo packages.

In 2016, AJ Styles made his WWE debut as third entrant into the Rumble. When his entrance revealed one word at a time, "I Am Phenomenal," the crowd exploded as one of the top talents in the world was now in WWE.

But not all debuts have to come from outside the WWE umbrella. With NXT becoming its own third brand, kept separate from Raw and SmackDown but still within the WWE galaxy, either full-time roster call-ups or a one-off appearance come into play.

Sami Zayn set the stage for his main roster call-up with a 2016 Rumble appearance that furthered his storyline with Kevin Owens. Last year, Tye Dillinger got the "Perfect 10" spot in the Rumble, and it wasn't long after that that he was part of the SmackDown Live roster.

No matter what category the return, the Royal Rumble's popularity has been fueled by unpredictability -- in terms of who will win and put on the best show, but just who is going to participate. And with so many open spots still remaining as the Rumble is just days away, WWE is capitalizing on the love of the unknown.