Barthel made his debut for Westside Xtreme Wrestling (wXw) in January 2009, under the ring name Axel Dieter Jr., losing to Dan Marshall.

[6] Dieter and Da Mack made 7 successful defences of the championship, defeating the likes of The Sumerian Death Squad (Tommy End and Michael Dante), Forever Hooligans (Rocky Romero and Alex Koslov) and Kazuki Hashimoto and Ryuichi Kawakami.

[8] After over a combined year as wXw World Tag Team Champions, Dieter and Da Mack were defeated by French Flavour (Lucas Di Leo and Peter Fischer) on 18 October 2014, bringing their reign to an end.

[11] In March, Dieter took part in the 16 Carat Gold Tournament, defeating Zack Sabre Jr. in the semi-final to advance to the final, where he lost to Tommy End.

[15] In late 2016, Dieter joined Ringkampf, and on 10 December, he defeated Marty Scurll to win the wXw Unified World Wrestling Title.

At the 17th Anniversary Show, in an untelevised segment, Barthel and Alexander Wolfe made the save on Walter and Thatcher after they were ambushed by members of the Rise stable.

[20] At the event, he teamed with Walter and Thatcher to defeat British Strong Style (Pete Dunne, Trent Seven and Tyler Bate).

[21] In March 2019, he participated in the 16 Carat Gold Tournament, defeating Marius Al-Ani in the first round,[22] before being eliminated by Lucky Kid in the quarter final.

[25] Representing wXw and Ringkampf, Dieter made his debut for Progress Wrestling in the United Kingdom on 15 January 2017, alongside Walter, defeating The London Riots (James Davis and Rob Lynch).

[37] On April 2, 2022 at NXT Stand & Deliver, they would lose the titles back to MSK in a triple threat tag team match also involving the Creed Brothers, ending their reign at 158 days.

[39] On the April 8 episode of SmackDown, Barthel, under the new ring name Ludwig Kaiser, debuted with Walter, now known as Gunther, accompanying him in a squash match against Joe Alonzo.

[41] On the May 27 episode of SmackDown, Kaiser had his first match on the main roster teaming with Gunther to defeat Drew Gulak and Intercontinental Champion Ricochet.

[46][47] On the August 30 episode of SmackDown in Berlin, Germany, Kaiser answered LA Knight's open challenge for the United States Championship, but failed to win the title.