3 times WWE has done the Lars Sullivan character before
#3 Sycho Sid
Active as a professional wrestler on and off from the late 1980s through late 2017, Sid Vicious had a career like few other performers. He was ultimately a two-time WWF World Heavyweight Champion and a two-time WCW World Heavyweight Champion beyond other titles with WCW, USWA, CWA and NWA. And if the rumors are true, he was asked to take Hulk Hogan's top babyface spot in the WWF in early 1990s, and declined such directly to Vince McMahon.
Sid changed his gimmick many times throughout his career. He was first Lord Humongous, working under a mask. He became Sid Vicious in WCW, initially working as a singles competitor before becoming one-half of The Skyscrapers. He became Sid Justice in the WWF in 1991, returned to WCW as Sid Justice in 1993, and would become Sycho Sid upon returning to the WWF in 1995.
As Sycho Sid, the performer was―of course―unstable and prone to attack other competitors including Shawn Michaels, who he was initially there to protect within his 1995 reintroduction to the WWF. Sycho Sid's theme song had minor-key string keyboard sounds meant to produce a chilling effect over industrial-metal music, comparable to the tack-piano sounds of Lars Sullivan's theme song.
Any way you slice it, the Lars Sullivan character has been done plenty of times before―to varying degrees of success―so hopefully there are plans for WWE to do more with the guy than have him forcefully take down babyface characters.