There's an old adage that says: "Father Time is undefeated." Truer words were never spoken, especially when it comes to pro wrestling. Unsurprisingly, retirement can be a slippery slope for a pro wrestler. Some performers have the foresight to call it quits while they still have plenty of gas left in their tank. Conversely, some performers have to be essentially forced to retire for their own good.

RELATED: The 5 Best & 5 Worst Retirement Matches, Ranked

Despite that, very few pro wrestlers actually manage to remain retired. Case and point being Terry Funk who has retired and unretired more times than fans can keep track of. In the end, some in-ring returns have proven to be extremely successful while others have proven to be ill-timed and ill-advised.

10 Successful: Edge

Edge Returns

2020 won't be remembered for its abundance of feel-good moments. However, before the wheels completely fell off, the year provided us with one of the best returns in WWE history. After retiring abruptly in 2011 and undergoing triple fusion neck surgery, Edge made his glorious return at Royal Rumble 2020. 

Entering the match at number 21, Edge managed to make it down to the final three competitors before being eliminated by Roman Reigns. The 23 minute plus performance was impressive considering Edge's nine-year hiatus. Edge would go on to wrestle only two more matches in 2020 before being sidelined with a torn triceps. Regardless, his shocking return from retirement won't soon be forgotten.

9 Bad: Shawn Michaels (2019)

After losing a "Career vs. Streak" match to The Undertaker at WrestleMania XXVI, Shawn Michaels closed the book on one of the greatest careers ever. For a while, it seemed as though Michaels would achieve the rare feat of remaining retired.

Unfortunately, in 2018, Michaels made the ill-fated decision to step back inside the ring. "The Heartbreak Kid" would team with his buddy Triple H to take on The Undertaker and Kane at WWE Crown Jewel 2018. The match wasn't pretty, to say the least. It was obvious that all four men were past their primes. Michaels hasn't wrestled since, and many fans hope things remain that way.

8 Successful: The Undertaker

Despite what WWE would like to have fans believe, The Undertaker retired after losing to Roman Reigns at WrestleMania 33. After the match, a clearly distraught "Deadman" took off his gloves and left them in the center of the ring, along with his hat and trench coat. The ugly truth about the matter is that if Vince McMahon wouldn't have asked The Undertaker to return, he would've more than likely remained retired.

RELATED: 10 Undertaker Dream Matches (That We Will Never See After His Retirement) 

In this particular scenario, however, fans should be thankful that The Undertaker didn't go out on such a low note. The instant classic that was the Boneyard Match against AJ Styles at WrestleMania 36 was a much more appropriate ending to such an iconic career.

7 Bad: Bruno Sammartino

After a legendary career that included a combined 11 years as WWWF World Champion, Bruno Sammartino's 1981 retirement was well deserved. Sammartino, who had been the centerpiece of WWE's predecessor, the World Wide Wrestling Federation, would join the promotion as a full-time color commentator in 1984.

Around this time, Sammartino made it a priority to help get his son David Sammartino over with the audience. Bruno even went as far as coming out of retirement to team with his son. Despite a couple of bright spots, Bruno Sammartino's return from retirement ultimately failed to accomplish its main objective of getting his son over with the fans. Sammartino would once again retire in 1987 and remain with WWE until 1988.

6 Successful: Ricky "The Dragon" Steamboat

Ricky "The Dragon" Steamboat is considered by many fans to be one of the best in-ring technicians ever. After a Hall Of Fame career, the former NWA World Champion was enjoying his legendary status before deciding to come out of retirement in 2009.

Steamboat would team with "Superfly" Jimmy Snuka and "Rowdy" Roddy Piper to face Chris Jericho at WrestleMania 25 in a three-on-one Handicap Elimination Match. Steamboat's participation in the match was originally an afterthought but, when the spotlight shined on The Dragon, he delivered a vintage performance. Steamboat's performance was impressive enough to earn him a one-on-one match with Jericho the following month at Backlash. His advanced age made it almost impossible for Steamboat to have a lengthy return, but that didn't diminish the quality of his impressive performances.

5 Bad: Ric Flair

At WrestleMania XXIV, "Nature Boy" Ric Fair retired at the top of his game, in a classic match against Shawn Michaels. Unfortunately, this was one of those scenarios where the retirement decision was made for the performer. Unsurprisingly, Flair's retirement didn't last. He would sign a one year deal with TNA in 2010.

At first, Flair was just used in a none contact role. Eventually, however, Flair couldn't resist the urge to step back in the ring. Unlike his critically acclaimed match with Shawn Michaels, Flair's TNA matches were almost cringeworthy. Mercifully, Flair would finally hang it up in 2011, following a torn triceps.

4 Successful: Daniel Bryan

When Daniel Bryan was forced to prematurely retire in 2016, the wrestling world felt like it was robbed of one of the greatest performers of this generation. At the time, Bryan was at the absolute peak of his career, having won the WWE World Heavyweight and Intercontinental Championships at consecutive WrestleMania events.

RELATED: Daniel Bryan's 5 Best Matches Before Retirement (& His 5 Best Since Coming Back)

Bryan would remain a part of the show, becoming SmackDown General Manager later in 2016. In 2018, after all hope of a potential return seemed to finally be gone, Bryan announced his return to the ring. At WrestleMania 34, Bryan would resume his career, tagging with Shane McMahon to take on Kevin Owens and Sami Zayn. He would enter the following WrestleMania as the WWE Champion, culminating his fairytale return.

3 Bad: Mick Foley (2000)

Foley v Rock

After falling through the roof of Hell In A Cell for the second time in two years, Mick Foley retired from wrestling in 2000. "The Hardcore Legend" had given the sport everything he had to give and had gotten just about everything he ever dreamed of in return. The one thing left on Foley's career bucket list was competing in the main event of WrestleMania.

At WrestleMania 2000, just six weeks after retiring from in-ring competition, Foley would make his return. Foley would be part of a Fatal Four Way main event for the WWE Championship. Regrettably, Foley was admittedly in poor shape for the match. He would go back into retirement after the match but would return a couple more times over the years.

2 Successful: Shawn Michaels (2002)

When Shawn Michaels came back from a four-year retirement at SummerSlam 2002, many fans had no idea what to expect. Michaels had been a generational talent before being forced to retire early, but returning after such an extended break from wrestling was no easy task.

To the surprise of many fans and critics, Michaels returned and didn't show any trace of being rusty. Michaels hadn't lost a step and was clearly still capable of stealing the show. Michaels would continue his impressive return at Survivor Series 2002, winning the World Heavyweight Championship in the first-ever Elimination Chamber match. From there, Michaels embarked on the greatest second act in wrestling history.

1 Bad: Bret Hart

When Bret Hart left WWE in 1997 amidst the controversy that was The Montreal Screwjob, not many fans expected him to ever find his way back to the promotion. In 2010, to the shock of many fans, Bret "The Hitman" Hart returned to WWE to bury the hatchet and finally move on from The Montreal Screwjob.

Part of the healing process included facing Vince McMahon in a Street Fight at WrestleMania XXVI. Hart would emerge victoriously, but it would be one of the worst matches in WrestleMania history. Sadly, Hart was no longer able to deliver extraordinary performances due to his health issues. Despite that, WWE wouldn't hesitate to continue booking him in marquee matches. Hart's legacy in pro wrestling is pretty well secured but his 2010 was a definite misstep on his part.

NEXT: Never Say Never: 10 Wrestlers Who Returned From Retirement