On the May 22, 2019 episode of NXT UK, Walter won a rematch for the United Kingdom Championship against Pete Dunne, after interference by Fabian Aichner and Marcel Barthel, thus establishing himself as a heel forming the stable known as Imperium. The faction would later be joined by Alexander Wolfe, after he interfered in a match pitting Imperium against British Strong Style (the team of Dunne, Tyler Bate, and Trent Seven). On the June 26 episode of NXT UK, Walter retained his title against Travis Banks. On the July 3 episode of NXT UK, Imperium interfered in Moustache Mountain's title match against Grizzled Young Veterans, therefore making Grizzled Young Veterans retain their titles. After the match, they injured Tyler Bate. On August 31 at NXT UK TakeOver: Cardiff, Walter retained his title against Tyler Bate.
In the build-up for the NXT UK and NXT co-branded pay-per-view, Worlds Collide, Imperium began feuding with The Undisputed Era (NXT Champion Adam Cole, Roderick Strong, and NXT Tag Team Champions Bobby Fish and Kyle O'Reilly), which was further intensified during the closing moments of NXT UK TakeOver: Blackpool II on January 12, 2020, when the group attacked Imperium following Walter's successful title defense against Joe Coffey. During Walter's reign the following week, the WWE United Kingdom Championship was renamed to the NXT United Kingdom Championship, and he was presented with a slightly updated belt design, replacing the WWE logo at the center with the NXT UK logo. On May 13, 2020, Barthel and Aichner defeated Matt Riddle and Timothy Thatcher (a substitute for Pete Dunne) to win the NXT Tag Team Championships after Thatcher walked out on Riddle. The duo retained the titles successfully against Breezango (Fandango and Tyler Breeze) before eventually losing the titles to the duo.
On the May 18, 2021 episode of NXT, after Wolfe was defeated by Killian Dain, he was attacked by Aichner and Barthel, thus kicking him out of the faction. At NXT TakeOver: 36, Walter dropped the United Kingdom Championship to Ilja Dragunov in a rematch, ending his historic reign at 870 days. At NXT Halloween Havoc, Aichner and Berthel regained the NXT Tag Team Championship by defeating MSK. They would later lose the titles back to MSK at Stand and Deliver the following year, in a triple threat match that also involved The Creed Brothers. Their final NXT appearance was on the April 5, 2022 episode of NXT, when Aichner and Barthel faced the Creed brothers in a losing effort, with Aichner walking out of their match, and Gunther (a renamed Walter) facing NXT Champion Bron Breakker in a losing effort.
On April 8, Gunther and Barthel (now going by Ludwig Kaiser) debuted on SmackDown for the first time, with Gunther defeating Joe Alonzo in his first match; while their association was maintained, the Imperium name was dropped. On the May 27 episode of SmackDown, Gunther and Kaiser made their debut as a tag team against Drew Gulak and Ricochet, with Kaiser pinning Gulak for the win. On the June 10 episode of SmackDown, Gunther defeated Ricochet to win the Intercontinental Championship, making him the first Austrian to win the title. Prior to Gunther's title defense at Clash at the Castle, Kaiser announced the reformation of Imperium by reintroducing Aichner, now known as Giovanni Vinci. Gunther subsequently defeated Sheamus to retain the Intercontinental Championship. At Extreme Rules on October 8, Imperium lost to The Brawling Brutes in a six-man tag team "Good Old Fashioned Donnybrook" match. On night two of WrestleMania 39, Gunther successfully defended the Intercontinental Championship against Sheamus and Drew McIntyre in a triple threat match.
As part of the 2023 WWE Draft, Imperium were drafted to the Raw brand.