#1 Jeff Jarrett

It is still incredible to say that Jeff Jarrett is now in the WWE Hall of Fame. Although he certainly has the career to earn it, he left WWE under the worst circumstances possible, enough to be blacklisted by the company forever, and was even legitimately fired from WCW/WWE on live television. Jeff would even start his own competing wrestling company TNA, who although never had the ratings they needed, were still a thorn in WWE's side for several years.
A Royal Rumble cameo for Double J is well earned and as he hasn't wrestled for WWE since No Mercy 1999, it would be really cool to see. The former 10 time World Champion can still hold his own in the ring and is a name that everyone still knows and would totally pop big for if he entered the match.
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Jeff could also be a valuable asset to WWE, so an appearance in the Royal Rumble match could lead him back to WWE to work backstage and as a TV performer in some capacity. Regardless, a Jeff Jarrett appearance in the Royal Rumble match would go down well with everyone.