Boxing legend Muhammad Ali played a huge role in the success of WWE and is one of the reasons that WrestleMania is the spectacle that it is today.
He was a special guest referee for the main event of the very first WrestleMania in 1985. The bout was a tag team match between Hulk Hogan and Mr. T against "Mr. Wonderful" Paul Orndorff and "Rowdy" Roddy Piper. During a brawl between the four wrestlers, Ali jumped in the ring and took a swing at Piper.
Ali had numerous other appearances in wresting, but none of those could top his appearance at the first WrestleMania.
The Ball Family
LaVar Ball has been cutting promos fitting of a wresting ring for most of the past year, so it's only appropriate that WWE arranged for him to make an appearance when "Monday Night Raw" just happened to be in Los Angeles a few days after his son Lonzo went to the Lakers with the second pick in the 2017 NBA Draft.
LaVar, Lonzo and younger brother LaMelo were part of a segment with WWE superstar The Miz, who ended up getting mad that he couldn't have a partnership with Big Baller Brand. Things quickly got out of hand (and somewhat controversial), and LaVar ended up acting as if he was going to fight Miz.
New England Patriots tight end Rob Gronkowski and WWE superstar Mojo Rawley are really good friends, and this showed when he came out to help Rawley win the Andre the Giant Memorial Trophy at this year's WrestleMania 33.
When WWE superstar Jinder Mahal threw a drink at Gronk, Gronkowski came out to get payback. He went into the ring and ran right through Mahal, helping Rawley get enough momentum to win the match.
To make matters worse for Mahal, a few weeks later on "Smackdown Live," Gronk threw his drink in Mahal's face.
Floyd Mayweather Jr.
Boxer Floyd Mayweather Jr. has had numerous run-ins on WWE, but the biggest appearance was when he beat Big Show at WrestleMania XXIV in 2008. In a No Disqualification match, Mayweather brought an entourage with him to the fight. Mayweather was able to knockout Big Show, using brass knuckles, to stay undefeated in his career.
Former NBA star Shaquille O'Neal's appearances have left a lot to be desired, as he has teased a feud with WWE superstar Big Show but to this point nothing has happened.
On two occasions, O'Neal has had a confrontation with the Big Show, once on Raw in 2009, and once during the Andre the Giant Memorial Battle Royal at WrestleMania 32 in 2016. Both Big Show and O'Neal teased a showdown at WrestleMania 33, but the match never came to be.
At WrestleMania 2 in 1986, the Bears' William Perry was involved in a WWE superstar and NFL player Battle Royal. Perry and the Bears had just won Super Bowl XX a few month earlier, so "The Fridge" had the attention of the crowd in Chicago. Perry wasn't able to win the match, as he was eliminated by Big John Studd. As payback, Perry faked a handshake with Studd and pulled him over the rope to eliminate Studd.
Perry was inducted into the WWE Hall of Fame's "Celebrity Wing" in 2006.
Baseball legend Pete Rose had numerous run-ins with WWE superstar Kane. He appeared at WrestleMania XIV in 1998, WrestleMania XV in '99 and WrestleMania 2000. All three of his appearances were focused on the made-for-PPV rivalry he had with Kane.
The two dropped their rivalry for a time in 2004, when Kane introduced Rose as the first celebrity inducted into the WWE Hall of Fame and Kane joked that Rose's stats showed this was the wrong hall of fame.
In 2015, Ronda Rousey was at the top of her UFC career when she stepped in the wrestling ring, and she definitely wasn't going to be pushed around at WrestleMania 31.
During a promo being cut by Stephanie McMahon, daughter of chairman Vince McMahon, and her husband Triple H, The Rock decided to come out and shut them up. After getting slapped by Stephanie, The Rock got Ronda Rousey to come out of the crowd and help him. Rousey threw a Judo toss on Triple H and proceeded to throw Stephanie out of the ring as well.
NFL Hall of Famer Lawrence Taylor's appearance stands out among the rest, and it's highly debated whether his appearance was for the better or worse as it relates to WWE's reputation.
While others on this list have had a match at WrestleMania, Taylor was in the main event at WrestleMania XI in 1995, against WWE superstar Bam Bam Bigelow. While Bigelow seemed to be destroying Taylor for most of the match, Taylor turned the tide and ended up beating Bigelow.
Another athlete in the WWE Hall of Fame, boxing legend Mike Tyson played a large role in WrestleMania XIV in 1998, as he was the "special enforcer" in a WWE title match between superstars Shawn Michaels and "Stone Cold" Steve Austin.
While Tyson was aligned with Michaels through the feud, he ended up counting the pin that gave Austin the victory and the belt. On top of that, Tyson knocked out Michaels after the match.