In May 2015, it was reported that Rezar had signed a contract with WWE and would begin training to become a professional wrestler at the WWE Performance Center. In October 2015, WWE confirmed that Rezar was a WWE developmental recruit already training at the Performance Center. He made his in-ring debut at an NXT house show in Venice, Florida on 30 January 2016, losing to Josh Woods. By February 2016, Rezar, under his real name Gzim Selmani, had formed a tag team with Sunny Dhinsa, and they became known as The Authors of Pain by April 2016.
Selmani and Dhinsa made their televised NXT debuts on 8 June 2016 at NXT TakeOver: The End; following the NXT Tag Team Championship match, they attacked champions American Alpha (Chad Gable and Jason Jordan) before leaving backstage with Paul Ellering. On the 15 June episode of NXT, the Authors of Pain won their first televised match and were managed by Ellering. On the 24 August episode of NXT, Selmani's ring name was revealed to be Rezar, while Dhinsa was billed as Akam. The duo won the 2016 Dusty Rhodes Tag Team Classic, defeating TM61 in the tournament final at NXT TakeOver: Toronto. At NXT TakeOver: San Antonio, the Authors of Pain defeated #DIY to win the NXT Tag Team Championship. They retained the title at NXT TakeOver: Orlando by defeating #DIY and The Revival in a Triple Threat Tag Team Elimination match by eliminating both teams. At NXT TakeOver: Chicago, the duo participated in the first NXT Takeover main event for the NXT Tag Team Championship by defeating #DIY in a ladder match to retain the title. At NXT TakeOver: Brooklyn III, the Authors of Pain lost the titles to SAnitY. At NXT TakeOver: WarGames, Authors of Pain and Roderick Strong competed in a 3-team WarGames match which was won by The Undisputed Era. At NXT TakeOver: Philadelphia, Authors of Pain got a tag title rematch but were unsuccessful. At NXT TakeOver: New Orleans, Authors of Pain competed in a Triple threat tag team match for the NXT Tag Team Championship and Dusty Rhodes Tag Team Classic trophy which was won by The Undisputed Era (Adam Cole and Kyle O'Reilly).
On the April 9, 2018 episode of Raw, The Authors of Pain, along with Ellering, made their main roster debut, defeating Heath Slater and Rhyno. After the match, Akam and Rezar ended their partnership with Ellering by pushing him away and leaving him ringside as they returned backstage. On the September 3 episode of Raw, The Authors of Pain, now under the shortened name of "AOP", were accompanied to the ring by the 205 Live General Manager, Drake Maverick, who announced himself as their new manager.
On the November 5 episode of Raw, The Authors of Pain defeated Seth Rollins in a handicap match to win the Raw Tag Team Championship for the first time. They went on to defeat SmackDown's Tag Team Champions Cesaro and Sheamus in an interbrand Champion vs Champion match at Survivor Series. They lost the titles to Bobby Roode and Chad Gable on 10 December episode of Raw. In January 2019, Akam suffered an undisclosed leg injury that reportedly would keep him out for “at least a few months”. He and Akam returned to action at Super ShowDown on 7 June 2019.
In September 2019, AOP began appearing in vignettes, warning of their return. During the 2019 WWE Draft in October, AOP went undrafted, becoming free agents and able to choose which brand to sign with. Three days after the draft's conclusion, AOP signed with Raw, remaining on the brand. On the Raw directly after Survivor Series, AOP returned as Seth Rollins' hired hands in his feud with Kevin Owens. In March 2020, it was reported that Rezar suffered a bicep injury and the injury would sideline him for six to eight months. On September 4, 2020, AOP were released from their WWE contracts before ever returning to television.
During the December 22, 2023 episode of SmackDown, Akam and Rezar were shown in a vignette alongside Karrion Kross and Scarlett, signaling their return to the company. The following week, during SmackDown New Year's Revolution on January 5, 2024, AOP officially returned alongside Kross, Scarlett and their old manager Paul Ellering, and attacked Bobby Lashley and the Street Profits (Angelo Dawkins and Montez Ford). AOP made their return to the ring on the February 16 edition of SmackDown, where they faced Beau Morris and Javier Bernal in a squash match. On night two of WrestleMania XL, the stable lost against The Pride (Bobby Lashley, Angelo Dawkins and Montez Ford) in a Philadelphia Street Fight. On the following episode of NXT, The Final Testament made their NXT return with AOP attacking Axiom and Nathan Frazer, who had just won the NXT Tag Team Championships from Baron Corbin and Bron Breakker.
During night two of the WWE Draft on April 29, Akam was drafted to Raw with the rest of The Final Testament.