IRS, as Mike Rotunda, and Barry Windham joined the World Wrestling Federation as The U.S. Express in 1984. They won the WWF World Tag Team Championship twice, first from Dick Murdoch and Adrian Adonis in January 1985. The U.S. Express' most notable feud was with The Iron Sheik and Nikolai Volkoff, to whom they lost the title at the first WrestleMania. The U.S. Express regained the belts in June 1985, but lost them two months later to Brutus Beefcake and Greg Valentine. Windham left the WWF soon after.
Rotunda continued to wrestle in singles matches until he left the WWF himself, in early 1986. He briefly returned to the WWF in the fall of 1986 to team with "Golden Boy" Dan Spivey as a new version of "The U.S. Express", but they were more or less used as a jobber team against up and coming teams such as Demolition in house shows.
The U.S. Express reunited in the American Wrestling Association (AWA) to wrestle at WrestleRock '86 on April 20, 1986, defeating The Fabulous Ones. The team did not stay long as Windham left the AWA very shortly after debuting. Rotunda stayed around for a few more months with little success.
In late 1987, Rotunda joined World Championship Wrestling (WCW), where he lingered at mid-card level as a face before turning heel and joining Kevin Sullivan's Varsity Club, a group of wrestlers with amateur wrestling credentials. Rotunda began bickering with fellow Varsity Club member Rick Steiner over which of the two had a superior alma mater. This in turn led to the two arguing over which of them was the superior wrestler.
Rotunda won the WCW World Television Championship from Nikita Koloff in January 1988. He then began a feud with Jimmy Garvin, because Sullivan wanted Garvin's wife Precious. Steiner left the group and began feuding with Rotunda, the enemies trading the Television Championship before Rotunda lost it to Sting.
"Dr. Death" Steve Williams and Dan Spivey joined the Varsity Club in late 1988, and Rotunda teamed with Williams to win the WCW World Tag Team Championship from The Road Warriors. Referee Theodore Long turned heel during the match and administered a fast three count, enabling Rotunda and Williams to overcome the champions. Long went on to become a manager following the controversial officiating.
In May 1989, Williams and Rotunda were stripped of the title and, shortly after Sullivan and Rotunda concluded a feud with the Steiner Brothers, Rotunda briefly left WCW. He returned in 1990 as a face, using the shipowner gimmick Captain Mike Rotunda. He formed a "crew" (consisting of Abdullah the Butcher and Norman the Lunatic) and feuded with Kevin Sullivan's new stable, "Sullivan's Slaughterhouse" (Cactus Jack, Buzz Sawyer, and Bam Bam Bigelow).
In mid-1990, Rotunda turned heel again and became Michael Wallstreet, with Alexandra York (and her computer) as his manager. They founded The York Foundation. The two claimed to know (via computer analysis) how to win each match and how long it would take for Wallstreet to become victorious. In this brief run he was undefeated and often a timer was present onscreen to further the duo's claim. The partnership ended when Rotunda left WCW in early 1991.
Rotunda returned to the WWF in April 1991, becoming Irwin R. Schyster, abbreviated to I.R.S.. Schyster had a heel gimmick as a former IRS tax collector from Washington, D.C., harassing wrestlers and fans as "tax cheats" and scolding them to "pay their fair share".
He made his pay-per-view debut at SummerSlam 1991, defeating Greg "The Hammer" Valentine. Schyster also made it to the finals of the 1991 King of the Ring tournament, defeating The Berzerker, Hacksaw Jim Duggan and Jerry Sags before losing to Bret Hart in the final match. He then had a short-lived feud with Big Boss Man in the fall of 1991. This culminated in a 6-man elimination tag team match at Survivor Series, where he teamed with The Natural Disasters in a losing effort against Boss Man and The Legion of Doom (the former Road Warriors). In January 1992, he competed in the Royal Rumble match, entering at number 18, and lasted 28 minutes.
In February 1992, Schyster formed the tag team Money Inc. with Ted DiBiase; the two won the WWF Tag Team Championship together three times. Money Inc.'s first title reign was at the expense of The Legion of Doom, making Rotunda the only wrestler to twice defeat them for a tag team title. They then feuded with the Natural Disasters, losing the titles to them and then regaining them a few months later. Finally, Money Inc. lost the tag team title to The Steiner Brothers twice. Ted DiBiase retired from wrestling to become a commentator in the summer of 1993, resulting in Schyster going back to singles competition.
In the beginning of 1994, IRS feuded with Razor Ramon, challenging him for the Intercontinental Championship at the Royal Rumble. Though Schyster had seemingly won the title after interference by Shawn Michaels, a second referee restarted the match, which Ramon won. Schyster then feuded with Tatanka, whom he accused of failing to pay a gift tax on a "sacred headdress" he received from Chief Jay Strongbow.
In mid-1994, he joined his former partner DiBiase's Million Dollar Corporation, often teaming with fellow member Bam Bam Bigelow, in an unsuccessful effort to regain tag team gold. Schyster later refocused on singles wrestling. His feud with The Undertaker included Schyster repossessing the headstone of a child, and interfering in a casket match between The Undertaker and Yokozuna. When the two eventually squared off at the 1995 Royal Rumble, the Undertaker was victorious following a chokeslam, but Schyster stole his urn after the match. I.R.S. then competed less frequently on WWF television, with his final two appearances being a loss to Savio Vega in a King of the Ring qualifying match in June 1995, and as a lumberjack the following month at In Your House 2: The Lumberjacks. Rotunda then left the WWF.
Rotunda returned to WCW in September 1995. On the debut of WCW Monday Nitro, which aired on September 4, 1995, he was introduced as Michael Wallstreet, but by the next episode he was known as V.K. Wallstreet with announcer Eric Bischoff asking Bobby Heenan on-air why his name had suddenly changed. Rotunda used the name for nearly a year while wrestling in a lower midcard position. The highlight of this run came at the 1996 Battlebowl, where he teamed with Jim Duggan and made it to the semifinals before losing to Dick Slater and Earl Robert Eaton. Eventually his name returned to Michael Wallstreet and Mr. Wallstreet, and in December 1996, he joined the nWo after being offered a membership by former tag team partner Ted DiBiase. While in the nWo, Wallstreet remained in the lower midcard. His highest profile match in this period was a loss to Jeff Jarrett at nWo Souled Out in January 1997. On the April 21 episode of Nitro, Wallstreet was forced out of the nWo when his nWo contract was declared null and void by James J. Dillon, due to his pre-existing WCW contract. Despite this, he appeared with the nWo weeks later on the May 5 Nitro, before finally accepting Dillon's ruling and leaving the group. Although no longer an nWo member, he openly expressed his contempt for WCW (frequently wearing anti-WCW T-shirts to the ring). In the summer of 1997, he left the WCW.
He returned (as Mike Rotunda) to WCW at Starrcade 1999, reforming the Varsity Club with Rick Steiner and Kevin Sullivan to team with Jim Duggan against The Revolution (Shane Douglas, Dean Malenko, Perry Saturn, and Asya). His team lost when they abandoned Duggan during the match. In early 2000, he took part in a "Lethal Lottery" tournament for the vacated WCW World Tag Team Championship, paired with Buzzkill. The two defeated Dean Malenko and Konnan in the first round, but lost in the quarterfinals to the Harris Brothers. Rotunda left WCW in the spring of 2000.
Rotunda was rehired by WWE as a road agent in 2006, and made several guest appearances as Irwin R. Schyster. One such appearance was on the August 6, 2007 edition of WWE Raw; Mr. McMahon was discussing his IRS troubles with Jonathan Coachman, and when the conversation ended, Schyster lowered the paper covering his face and revealed himself.
I.R.S. appeared on the December 10, 2007 15th Anniversary edition of Raw, winning a 15-man battle royal, only to be paid by his former tag team partner Ted DiBiase to eliminate himself and give DiBiase the win.
On the March 10, 2008 episode of Raw, The U.S. Express were to have a rematch from WrestleMania I against Nikolai Volkoff and The Iron Sheik. However, the match was interrupted before it could begin by diva Jillian Hall, who offered to sing "Born in the U.S.A." for them; she was given an airplane spin by Rotunda.
I.R.S. appeared on the September 7, 2009 edition of Raw, of which Bob Barker was the guest host. He was a contestant in a pricing game along with Santino Marella, Jillian Hall, and Chris Jericho, bidding on a "Best of SmackDown" DVD. I.R.S was, later that night, one of the contestants during the second round of the pricing game.
I.R.S. appeared on an episode of Monday Night Raw as a lumberjack in the "'80's Legend Lumberjack Match", in which Christian defeated Ted DiBiase. On the May 5, 2010 SmackDown, I.R.S. helped throw Drew McIntyre out of the arena. On June 7, 2010, I.R.S. appeared on Raw in a comedy segment. He announced he had taken Jerry Lawler's crown, because Lawler had not paid his taxes. On the June 28 Raw, he was one of the four people who entered the ring to celebrate Ricky Steamboat's career, but were attacked by the Nexus.
I.R.S. appeared on the April 9, 2012 edition of Raw. He, along with numerous other WWE officials and superstars, attempted to break up a brawl between Brock Lesnar and John Cena.
On the January 6, 2014 "Old School" episode of Raw, Irwin R. Schyster encountered Big E Langston on his way to a match and told him to pay his taxes, to which Langston smiled. Immediately prior, Langston walked past fellow Million Dollar Corporation members Nikolai Volkoff and Ted DiBiase.
On April 15, 2020, Rotunda was released from the WWE as a producer.
In January 2021, on Raw Legends Night, Rotunda, as I.R.S., made his first appearance since being released by the WWE in a segment backstage with Ric Flair. On January 23, 2023, Rotunda, as I.R.S., made a backstage appearance at Raw is XXX alongside Ted DiBiase.
On March 8, 2024, Rotunda, alongside with his former tag team partner and brother-in-law Barry Windham, under their U.S. Express tag team name, were announced as the first tag team inductee for the WWE Hall of Fame Class of 2024.