On August 14, 2019, Escobar signed a contract with WWE. During one of the first weeks while training at the WWE Performance Center, he suffered a knee injury that prevented him from wrestling for several months. He made his in-ring debut under his real name for NXT on February 15, 2020 teaming with Raul Mendoza to defeat Lewis Howley and Sam Stoker on a show in Fort Pierce, Florida. On April 12, 2020, Escobar, under the name El Hijo del Fantasma, was announced as a participant in the interim NXT Cruiserweight Title tournament, representing Group B in the tournament. In the finals, he defeated Drake Maverick to become Cruiserweight Champion for the first time, as well as winning his first championship in WWE. The following week, Fantasma joined forces with two masked men who, up to that point, constantly tried to attack multiple NXT superstars, and revealed themselves as Raul Mendoza and Joaquin Wilde. The threesome attacked Maverick, then Fantasma unmasked and adopted the new ring name of Santos Escobar, establishing himself as a heel in the process. Escobar then began feuding with Isaiah "Swerve" Scott, facing him on the August 26 episode of NXT and at NXT TakeOver: 31, retaining the title both times. At NXT Halloween Havoc, Escobar would defeat Jake Atlas in a non-title match. At NXT New Years Evil, Escobar would defeat Gran Metalik to retain his Cruiserweight Title. Escobar would then face Curt Stallion on the February 3 episode of NXT for the Cruiserweight title, and Escobar would win the match. Escobar would then enter a brief feud with Karrion Kross, which came to ahead on the February 24 episode of NXT in a no disqualification match, in which Escobar would lose.
On March 10, 2021, it was announced that Jordan Devlin, the original Cruiserweight Champion, who was unable to defend his title, would appear on NXT the following week to challenge Santos Escobar, deciding who was the undisputed Cruiserweight Champion in the process. This culminated on April 8, 2021, when Escobar defeated Devlin in a ladder match at NXT TakeOver: Stand and Deliver.
On the April 13 episode of NXT, he issued an open challenge, where he lost his title to Kushida, ending his reign at 321 days. After Escobar failed to regain his title from Kushida in a two-out-of-three falls match on the May 11 episode of NXT, he and the other members of Legado del Fantasma would begin feuding with NXT North American Champion Bronson Reed and NXT Tag Team Champions MSK, which would lead to a winners take all six-man tag team match at NXT TakeOver: In Your House, where Legado del Fantasma would be unsuccessful in winning the titles. Shortly after, Escobar would then start feuding with Hit Row, and on the August 24 episode of NXT, Legado del Fantasma would defeat Hit Row in a six-man tag team match with the help of a debuting Elektra Lopez. On the October 12 episode of NXT 2.0, Escobar would face Scott for the NXT North American Championship, but would be unsuccessful. After the match, Carmelo Hayes would cash in his NXT Breakout Tournament opportunity and win the North American Championship from Scott. In early 2022, Escobar would feud with NXT Champion Bron Breakker, unsuccessfully challenging for the NXT Championship at NXT Vengeance Day despite interference from Dolph Ziggler. At NXT Stand and Deliver, Escobar would fail to win the NXT North American Championship in a ladder match. Shortly after Stand and Deliver, Legado del Fantasma would feud with Tony D'Angelo, the self proclaimed "Don of NXT" and his "family".
During their feud with D'Angelo, they would slowly turn into faces while portraying heelish tactics. After multiple meetings and kidnappings, Escobar would defeated D'Angelo on the May 17 episode of NXT; however at NXT In Your House, Legado del Fantasma lost to the D'Angelo Family (Tony D'Angelo, Stacks and Two Dimes), with the losers having to join the other person's family. With Legado joining the D'Angelo Family, they would accompany each other during matches with them usually losing. On the June 21 episode of NXT, Escobar would cost D'Angelo his title match against NXT North American Champion Carmelo Hayes. At NXT The Great American Bash, it was revealed that Escobar was hospitalized and the other members of Legado began working with the D'Angelo Family. On the August 2 episode of NXT, Escobar would return and cost D'Angelo and Stacks their title match against The Creed Brothers, signaling that their alliance had come to an end. At NXT Heatwave, Escobar lost a street fight to D'Angelo, thus banning him from NXT.
On the October 7, 2022 episode of SmackDown, Escobar would make his main roster debut alongside Wilde and Del Toro, as Legado del Fantasma, when they attacked Hit Row before their scheduled match and aligned themselves with Zelina Vega. At the Royal Rumble on January 28, 2023, Escobar entered his first Royal Rumble match at number ten, but was eliminated by Brock Lesnar. On the February 10 episode of SmackDown, Escobar competed in a four-way match to determine the number one contender to the WWE Intercontinental Championship, which was won by Madcap Moss. After the match, during an exclusive uploaded to WWE's social media, Escobar would approach fellow competitor Rey Mysterio after the match, offering him one of his masks, and signifying a face turn. Following this, Escobar would find himself involved in the feud between Rey and his son Dominik Mysterio, assisting Rey in the feud against Dominik and The Judgment Day as a result, continuing the face turn in the process. On the March 3 episode of SmackDown, Escobar faced Dominik in a match and was defeated following interference from Rhea Ripley, after which Dominik tore up the mask Rey gave to Escobar, solidifying Escobar's face turn. On the March 31 episode of SmackDown, Rey reformed the Latino World Order and invited Legado del Fantasma to join as a token of appreciation for aiding him in his fight against Dominik and The Judgment Day, which they accepted.
On the June 9 episode of SmackDown, Escobar defeated Mustafa Ali to qualify for the men's Money in the Bank ladder match. Escobar and stablemate Zelina Vega failed to win their respective Money in the Bank ladder matches in the namesake event. Escobar then won a fatal four-way semifinal match in the United States Championship invitational tournament, going on to face fellow stablemate Rey Mysterio in the finals on the July 28 episode of SmackDown. During the match, Mysterio would suffer a minor injury scare, thus giving Escobar the win by forfeit. On the August 11 episode of SmackDown, Escobar was taken out by United States Champion Austin Theory before the match started. Due to Escobar's injury, WWE Official Adam Pearce allowed Rey to take Escobar's place for the title match, where he defeated Theory to become the new United States Champion. At Crown Jewel on November 4, Escobar costed Rey the United States Championship after he snatched away a brass knuckles from a member of Logan Paul's entourage and left it on the ring while chasing Paul's entourage away only for Paul to use it on Rey to win the match. On the November 10 episode of SmackDown, Escobar was accused by Carlito for purposefully leaving the brass knuckles at the side of the ring at Crown Jewel. After Carlito's match with Bobby Lashley, Escobar attacked Rey as Rey was checking on Carlito, turning heel and leaving the LWO in the process. On the following week's episode of SmackDown, Escobar entered using the Legado del Fantasma theme, where he chastised Rey for not sticking with him while kicking Vega, Wilde and Del Toro from Legado del Fantasma. A match between Carlito and Escobar was then announced for Survivor Series: WarGames, however, day before the event, Escobar took out Carlito in the ring and backstage. Dragon Lee would save Carlito from Escobar, allowing SmackDown General Manager Nick Aldis to permit Lee to face Escobar as Carlito's replacement at Survivor Series: WarGames. Escobar would win the match at the event. On the December 1 episode of SmackDown, Escobar defeated Joaquin Wilde and continued attacking him after the match, with Lee coming out to save Wilde. It was later announced that Lee would face Escobar in a United States Championship number one contender tournament the following week, which was won by Escobar. In the semifinals, Escobar defeated Bobby Lashley after interference from the returning Humberto Carrillo and Angel Garza. Escobar lost to Kevin Owens in the finals at SmackDown New Year's Revolution on January 5, 2024. Two weeks later, the newly revived Legado del Fantasma defeated Carlito, Wilde and Del Toro in a six-man tag team match. The following week, Elektra Lopez reunited with Escobar and returned to Legado del Fantasma. Escobar entered the Royal Rumble match at the titular event as the seventh entrant, but was eliminated by Carlito.
On the March 22 episode of SmackDown, Escobar and Mysterio would face off against each other with the stipulation of both members of the LWO and Legado del Fantasma being banned from ringside; Escobar would win after interference from “Dirty” Dominik Mysterio. Soon after, a tag team match between Rey Mysterio and Dragon Lee against Escobar and Dominik Mysterio was announced for WrestleMania XL. On the final SmackDown before WrestleMania, Lee was attacked backstage, leaving Andrade to take his place in the tag team match, would Escobar and Dominik would go on to lose on April 6.