Julio Lopez, codenamed Gulliver, is a member of the Mobile Armored Strike Kommand. Lopez is a combat surgery specialist, serving as the M.A.S.K. team's medic, and wears the Gulliver Mask. Lopez's primary vehicle is the Jackhammer, but he has also been known to drive the Rhino vehicle with Bruno Sheppard.
Julio Lopez was a former med student who had aspirations of being a doctor, but was also a fan of heavy metal music. His love of music led him to form a band called Cold Crawlers (providing lead vocals and guitars.) While he and his band were playing a show on Venice Beach, a couple of would-be thieves attempted to loot their van before being stopped by off-duty G.I. Joe member Rock 'n Roll. After the show, Julio thanked Rock and chatted with him about the difficulty of balancing music with med school. As they went their separate ways, Julio told Rock he hoped they might run into each other again. Ultimately, Julio was unable to balance his band and schoolwork, and flunked out. Shortly after that, his mother, Maya Lopez passed away. Julio decided to rededicate himself to helping others, and began working to medical services to in-need communities. During one of these ventures, he met and befriended Matt Trakker.
Julio was one of the recruits to Project Spectrum, along with Matt. After the recruits' first meeting with Miles "Mayhem" Manheim, Brad Turner asked Lopez what he thought Manheim meant by "washing out". Lopez was present for the first test drive of the Project Spectrum vehicles, as well as being given the opportunity to test the specialized Mask weapons, selecting the Gulliver Mask. Later, during a field test involving a train in the Canadian Rockies, Lopez was forced to stop Matt from rescuing a group a civilians from the train before it exploded. The test left him demoralized.
During M.A.S.K.'s first mission engaging the Autobots Kup and Aileron at Mount Olympus, Lopez drove the Rhino vehicle along with Bruno Sheppard. He continued his role as Rhino's driver during M.A.S.K.'s assault on Autobot City. After the fight, Lopez asked if anyone had seen Sheppard, Vanessa Warfield, or Sly Rax, presuming dead in the Ore-13 explosion.
After their conflict with the Transformers, M.A.S.K. ended up being framed for a series of crimes, forcing them to leave their old headquarters at Project Spectrum. After escaping from the authorities into "The Dutchman's Doorway", Julio expressed his concern about the danger of the Ore-13 powering M.A.S.K.'s equipment. While the team regrouped in one of Cornelius Trakker's secret labs, he detected a massive spike in Ore-13 energy in Barbados. When Brad showed up with a yacht to transport their vehicles, Lopez asked how he acquired it, only to be even more confused as to why drag dealers owed Brad favors. In Barbados, the team discovered the Ore-13 in Harrison's Cave, only for them to be attacked by a blue jet, which aimed to take out Julio first and leave them without a medic. The four ducked for cover inside the Cave... only to be attacked by V.E.N.O.M.! The M.A.S.K. team were shocked to see their presumed-dead comrades alive again. While Matt distracted V.E.N.O.M., Julio and Gloria pulled Brad out of the cave, escaping to their vehicles. He helped Matt run interference in the Jackhammer while Gloria returned Brad to the yacht.
The next morning, after stabilizing Brad, Lopez called Matt and Gloria down to the medical bay. He revealed that while examining Brad's blood, he detected low levels of radiation in his blood matching that of the Ore-13 that powered their equipment. This radiation was present in all the M.A.S.K. agents and was slowly going to kill them all. He then brought up the more pressing topic of their former teammates alive and working with Miles Mayhem. Matt said that they were taken by surprise this time, but next time, they would be ready for them.
- In the original toyline, Lopez's Mask was called "Streamer", while "Gulliver" was the name of the Mask worn by Calhoun Burns.