On August 23, 2018, Humberto Carrillo started competing for the WWE and signed his official contract on October 18, 2018, along with other recruits. Prior to that, Carrillo made an appearance on the September 19 edition of NXT against Jaxson Ryker in a losing effort.
On the December 5 edition of NXT, Carrillo would make his televised return when he teamed with Raul Mendoza in a losing effort against Steve Cutler and Wesley Blake of The Forgotten Sons. On the January 16, 2019 edition of NXT, Carrillo competed against Johnny Gargano in a losing effort.
On the January 15, 2019 edition of 205 Live, Carrillo made his main roster debut when he answered the WWE Cruiserweight Champion Buddy Murphy's open challenge in a losing effort. Despite this, General Manager Drake Maverick revealed after the show that Carrillo has joined the 205 Live Roster and will compete at the WWE Worlds Collide Tournament at the Royal Rumble Axxess. The following week, Carrillo scored his first win on the brand defeating Gran Metalik. On February 5, 2019, Carrillo competed in a fatal four-way elimination match to determine who would challenge Buddy Murphy for the WWE Cruiserweight Championship at Elimination Chamber, which Carrillo lost. On August 27, 2019, Carrillo defeated Oney Lorcan to earn a title shot against Drew Gulak for the WWE Cruiserweight Championship at Clash of Champions. At Clash of Champions, he was defeated by Gulak, in a triple threat match also involving Lince Dorado.
As part of the 2019 draft, Carrillo was drafted to the Raw brand. Carrillo made his debut on the October 21 episode, losing to WWE Universal Champion Seth Rollins. The following week on Raw, Carillo lost to WWE United States Champion AJ Styles. On October 31, 2019, on the Crown Jewel kickoff show, Carrillo won a 20-man battle royal to earn a WWE United States Championship match against Styles later that night, which was again in a losing effort. Carrillo would get his first win on the main roster, teaming with Ricochet and Randy Orton to defeat The O.C. (A.J. Styles, Karl Anderson, and Luke Gallows) on the November 11 Raw. On the December 16 episode of Raw, Carrillo competed in a #1 Contender's Gauntlet match for the United States Championship but was defeated by Andrade after he was unable to continue following a DDT on the concrete floor, which would sideline him for several weeks. He would return on the January 20, 2020 episode of Raw, saving Rey Mysterio from an attack by Andrade, thus setting up a match between Carrillo and Andrade for the United States Championship at the Royal Rumble, which Carrillo lost. In a rematch the following night on Raw, Andrade's manager Zelina Vega interfered and got Andrade disqualified, after which Carrillo snapped in a rage, and gave Andrade his own Hammerlock DDT signature move onto the exposed concrete, resulting in Andrade being written off due to injury.
Following this, Carrillo would begin a feud with his real-life cousin Angel Garza, who Vega introduced as her newest protégé, and proceeded to attack him on the February 3, 2020 episode of Raw. This set up a match between the two at WWE Super ShowDown, where Carillo was defeated by Garza. On the March 2, 2020 episode of Raw, Carrillo teamed with Mysterio to defeat Andrade and Garza where he pinned Andrade, earning himself a United States Championship match at Elimination Chamber. At the event, Carrillo was unsuccessful in capturing the United States Championship from Andrade. On the May 4 episode of Raw, Carrillo participated in a last chance gauntlet match to determine the final competitor in the Money in the Bank ladder match where he entered fifth, defeating Bobby Lashley by disqualification, Angel Garza, and Austin Theory, but lost to the returning AJ Styles.
He then began a feud with Seth Rollins after he injured his friend Rey Mysterio, challenging Rollins's disciple Murphy to a match on the May 18 episode of Raw where Carrillo lost. On the May 25 episode of Raw, Carrillo teamed with Aleister Black, where they were defeated by Murphy and Austin Theory after Theory pinned Carrillo. The following week, Carrillo accompanied Black in his match against Rollins where Black was victorious. After the match, Black and Carrillo were attacked by Rollins, Murphy and Theory and both received a Curb Stomp. On the June 29 episode of Raw, Carillo teamed with Aleister Black, where they were defeated by Buddy Murphy and Seth Rollins. After the match, Rollins and Murphy attacked Carillo and Black, which ended with Rollins performing a Curb Stomp on Carrillo onto the steel steps. On the July 27 episode of Raw, Carillo returned and faced Murphy where he was defeated. On the September 21 Raw, Carrillo teamed with Dominik Mysterio and fought Andrade and Angel Garza and Seth Rollins and Murphy in a triple threat tag match for a future Raw Tag Team Championship opportunity, but were defeated. Two weeks later on Raw, Carrillo once again teamed with Mysterio and fought Rollins and Murphy in a losing effort. Following this, Carrillo would wrestle exclusively on Main Event for the next several months.
Carrillo returned to television on the April 9, 2021 episode of SmackDown, participating in the André the Giant Memorial Battle Royal, which he failed to win. On the April 19 episode of Raw, Carrillo accepted Sheamus' open challenge for the United States Championship; however he was viciously attacked by Sheamus before the match began. The following week, he attacked Sheamus as revenge for what the latter previously did to him. Carrillo would face Sheamus for the title on the May 10 episode of Raw, which ended in referee stoppage after Carrillo injured his knee. Carrillo returned from injury on the May 24 episode of Raw, once again losing in a non-title match against Sheamus. He defeated him in another non-title match the following week, after Sheamus had just lost to Ricochet. On the July 5 episode of Raw, it would be announced that Carrillo would face Sheamus for the United States Title on next weeks episode, but he would go on to lose the match.
On the September 20 episode of Raw, Carrillo formed a tag team with his cousin Angel Garza, showing a more aggressive style, thus turning heel in the process. The following week on Raw, he helped Garza defeat Erik, cementing his heel turn. On the October 4 episode of Raw, Carrillo and Garza were drafted to the SmackDown brand as apart of the 2021 WWE Draft. On the November 5 episode of SmackDown, the team was officially dubbed Los Lotharios, with both Carrillo and Garza having shortened their ring names, being billed as Humberto and Angel.
As part of the 2023 WWE Draft, Angel, along with Humberto, was drafted to the Raw brand. However, before they would make their first appearance on the red brand, Los Lotharios returned to television on the June 13, 2023 episode of NXT, attacking Axiom and Scrypts after their win against Dabba-Kato. Humberto would then revert his name back to Humberto Carrillo. Carrillo, with Garza, returned on the December 22 episode of SmackDown, aligning with Santos Escobar. On the January 19, 2024 episode of SmackDown, the newly revived Legado del Fantasma defeated Latino World Order's Carlito, Joaquin Wilde and Cruz Del Toro in a six-man tag team match. On February 2, Carrillo's ring name was shortened to Berto. On the November 15 episode of SmackDown, United States Champion LA Knight announced an open challenge for the title, which was accepted by Legado del Fantasma. Knight then gave the title shot to Berto, but he failed to win the title.