NXT (2017–2020)

In January 2017, WWE pulled a contract offer from Dijak, following a legal threat from ROH, who still had him under contract.^[18] The following month, Dijak opted not to re-sign with ROH, essentially putting his career on hold, waiting for another contract offer from WWE.^[18] On July 20, it was reported that Dijak was finishing up his independent bookings ahead of joining WWE.^[18] Dijak reported to the WWE Performance Center on August 21.^[19] His signing was announced by the company on September 5.^[20]

Dijak made his debut for WWE's developmental branch, NXT, on September 23.^[21] His television debut, under his real name, came on May 30, 2018, in a loss against Ricochet. In July 2018, WWE revealed Dijak's new ring name as Dominik Dijakovic. Promos started to appear on the December 5, 2018 episode of NXT, promoting the debut of Dominik Dijakovic. Dijakovic made his debut as a villain on the December 19 episode of NXT, defeating Aaron Mackey.^[22] Following WrestleMania 35, he was set to feud with then NXT North American Champion Velveteen Dream over the championship. However, in April 2019, he suffered a torn meniscus that would require surgery.^[23] He would be out of action until late July, when he returned at an NXT live event.^[24]

On November 13, 2019 episode of NXT, Dijakovic turned face when he joined Team Ciampa for the annual WarGames match with Tommaso Ciampa, Matt Riddle and Keith Lee against The Undisputed Era at TakeOver: WarGames. Riddle proceeded to leave the team to pursue his rivalry with Finn Bálor.^[25] At the event, Dijakovic and Team Ciampa defeated The Undisputed Era, with Riddle's place being taken by Kevin Owens.^[26] On the January 29, 2020 episode of NXT, Dijakovic defeated Damian Priest to become the number one contender for Keith Lee's NXT North American Championship at TakeOver: Portland on February 16, where he failed to win the title. After the match, Lee and Dijakovic shook hands as a sign of respect.^[27] After Lee's NXT Championship win against Adam Cole at The Great American Bash, Dijakovic was challenged by Lee for both the NXT Championship and NXT North American Championship on the following episode, but was unsuccessful in capturing the titles. He was then attacked by Karrion Kross during a backstage interview, resulting in a match between the two on the July 22 episode of NXT, which Dijakovic lost. This marked his final appearance on NXT.

Retribution (2020–2022)

On the September 21 episode of Raw, he was revealed as a member of the villainous stable Retribution, under the ring name T-Bar, with a new outfit and a mask.^[28] On the October 5 episode of Raw, Mustafa Ali was revealed as the stable's leader. Over the following weeks, the faction had little success. At Fastlane on March 21, 2021, T-Bar and Mace attacked Ali, disbanding the stable. On the April 12 episode of Raw, T-Bar and Mace attacked Drew McIntyre, showing signs of joining The Hurt Business. The following week on Raw , T-Bar was finally unmasked along with Mace in a tag team match against McIntyre and Braun Strowman, in which T-Bar and Mace won by disqualification. Later in an interview, they confirmed the start of their tag team run. After a few weeks of absence from television, T-Bar and Mace were put as lumberjacks in a Lumberjack match between John Morrison and Damian Priest on the May 17 episode of Raw.

As part of the 2021 Draft, Mace was drafted to the SmackDown brand while T-Bar remained on the Raw brand, thus disbanding the team.^[29] On the October 25 episode of Raw, T-Bar got himself disqualified in a match against WWE United States Champion Damian Priest after throwing an office chair at the champion.^[30] On the November 1 episode of Raw, he lost to Priest in a no disqualification match in which Priest retained the US title.^[31] Throughout 2022, he was relegated to competing on WWE Main Event until October.

Return to NXT (2022–present)

On the October 25 episode of NXT, a vignette was shown of T-Bar's Retribution mask being tossed into a fire, teasing his return to the NXT brand. On the November 22 episode of NXT, he returned to the brand, now repackaged as a Terminator-inspired character under the Dijak name, and attacked Wes Lee after Wes successfully defended the NXT North American Championship against Carmelo Hayes.^[32][33] At Vengeance Day, Dijak lost his NXT North American Championship match due to interference from Tony D'Angelo and fellow NXT superstar Channing "Stacks" Lorenzo, thus giving Wes Lee the opportunity to capitalise on the distraction and retain the championship.^[34] On March 7 at Roadblock, Dijak was defeated by D'Angelo in a Jailhouse Street Fight.^[35] In April, Dijak began a feud with Ilja Dragunov.^[36] At Spring Breakin', Dijak attacked Dragunov backstage.^[37] At Battleground on May 28, Dijak was defeated by Dragunov in a Last Man Standing match, ending the feud.^[38]

On the November 7 episode of NXT, Dijak defeated Tyler Bate to qualify for the Iron Survivor Challenge at Deadline,^[39] which was won by Trick Williams.^[40] On the January 15 episode of NXT, Dijak faced Trey Bearhill, with Joe Gacy serving as commentator. During the match, Gacy headbutted Dijak. After Dijak won the match against Bearhill, Gacy attacked Dijak from behind and both men started brawling.^[41] The following week, a match between Dijak and Gacy was scheduled, but the match didn't happen due to Gacy attacking Dijak before the bell rang. Both men continued fighting until they were pulled apart by referees and security guards.^[42] On February 4, 2024 at Vengeance Day, Dijak defeated Joe Gacy in a No Disqualification match.^[43] During Dijak's matches after Vengeance Day, Gacy started appearing under the ring apron. On the February 13 episode of NXT, Gacy faced Carmelo Hayes in a losing effort. After the match, Dijak attacked Gacy with a nightstick and then locked him in a straitjacket and left.^[44] The following week, Dijak locked Gacy in an asylum cell, with Gacy laughing and telling Dijak that "this wasn't over".^[45] On the February 27 episode of NXT, Dijak defeated Luca Crusifino. After the match, Gacy ripped apart the straitjacket and started beating down Dijak until both men went backstage, where they continued fighting.^[46] On March 5 at Roadblock, Dijak defeated Gacy in an Asylum match.^[47] At Stand & Deliver on April 6, Dijak failed to win the NXT North American Championship from Oba Femi in a triple threat match which also include Josh Briggs.^[48]