The most important thing is, the monsters are sent by people. Terrible people! That's why I built Mech-X4. So you could stop them, Ryan.

Leo Mendel is the creator of Mech-X4. His current location is unknown, but he's revealed to be alive and held hostage. He left various video messages behind for the boys to discover, but they have yet managed to find out who he really is.


Leo was the one who created Mech-X4 some time prior to the events of Let's Call It Mech-X4!. He has warned that the Mech-X4 team monsters are coming and that Mech-X4 was built to defend the city. He knew that Ryan was a Technopath since birth, and that he'd be the one to discover Mech-X4. For Ryan's safety, he anonymously put him up adoption. It's shown in Let's Get Some Air!, he is being held captive by the creator of the monsters, who is later found out to be Seth Harper. It is also revealed he built a failed prototype of Mech-X4 called Mech-X3, which was piloted by Leo OS and was scavenged for parts in the second half of season one.


Season 1

In Let's Get Some Air!, Leo is held captive by the The Mastermind.

In Let's Get Some Answers!, Leo was still held captive by the Mastermind and the guards feed him lunch. The Mastermind took his lunch because he didn't say who the pilots of Mech-X4 were. Leo used the spork (spoon and fork) to get him out of the locked room. He got captured by the guards and got thrown back into his locked room.

In Let's Get Leo!. The Mastermind reminded Leo that nobody is going to rescue him since they don't know where he is. Leo got rescued by Ryan and used Spyder's Mech Link. Mark got Leo into the Med Bay.

In Let's Dig Deep!, Leo told Ryan, Mark, Harris and Spyder there is a giant pocket of Primorphous Gel. They needed to get to it first before Seth. Leo came up with a plan to get into Seth's brain to figure out where the Primorphous Gel is. Leo gave Harris and Spyder the device that will get into Seth's brain and out. Ryan and Mark contacted Leo and he reminded him that he could get brain damage if he stays there too long.

In Let's Destroy Some Ooze!, Leo was in Mech-X3 getting the drill fixed onto Mech-X4 with Ryan. Leo told Ryan about why his birth parents left him and why he was put onto adaption. Leo advised Ryan not to go to Harper Futuristics, but he went anyway.

In Let's End This! Part One, Leo saw that a missile hit Mech-X4. Ryan and Spyder threw it outside. Leo told Ryan that he had to stop the missiles with his powers and that he was lucky that he was the technopath. Leo and Spyder tried to on the power. Leo got the power on, but ended up injuring himself.

In Let's End This! Part Two, Grace woke up and found out who the pilots were. Ryan called his team because Grace went to the monster. Later, Leo and Harris were fixing any damage that was done to Mech-X4. Leo was with Grace at the Med Bay. He was watching her just in case she doesn't find out that Ryan was in the control room.

Season 2

In Versus The Deep, Harris called Leo about the Mech Sub. Harris checked if he was at the Ferry Hanger and jumped out to scare Harris. Leo showed Harris the blueprints for the Mech Sub. Leo and Harris needed to get extra equipment so they went to the Decommissioned Submarine Yard. Leo and Harris got caught by security guards. One of the security guards saw that there was a drone in their bag. Leo and Harris tried to lie about who they were, but the security guards weren't convinced because Harris was a child. Leo asked the drone to attack which made them shoot lasers at the security guards. They escaped and got the parts they needed. They built the Mech Sub and it docked in on Mech-X4. Leo was still on the Mech Jet whilst Harris came to the control room.

In Versus Harper's Ghost, Leo and Ryan were finding Ryan's father. Leo recognized Randall Anthony through the pictures and Ryan told him that he was his biological father. Leo alerted Ryan that he found Randall's location. If they don't save him, Randall might be gone forever.

In Versus The Mountain, Leo was talking with Ryan more about Randall. Leo showed Ryan, Harris and Mark the Home Defense Unit. He explained that if they put it on Grace's house, it would be able to detect Grey or Seth. Leo showed Mark the Markmobile Leo made because he didn't want Mark to feel left out. Mark asked Leo if he could be a technopath to so he could help Ryan. Leo and Mark were on the roof installing the Home Defense Unit and Mark was still questioning if he could be a technopath. Grace came home and saw Leo and Mark were on her roof. They lied that Leo was the repairman. Leo told Mark that he gave Ryan to Mark's family because of Mark. The lights in the garage turn off and Mark wondered if they did that.

In Versus The Dark Night, Leo was figuring what was happening to Bay City but he fell asleep on a park bench. He came back in Mech-X4 and turned the power on due to Veracity's generator.

In Versus Traeger, Leo and Harris showed Ryan and Spyder the new weapon they have been working on which could defeat Traeger. Leo left to go get technology for the Mech Jet so they could defeat any flying monsters. Leo was offered something to eat and he almost revealed himself. Leo spotted Aaron and tried to hide from him. Aaron captured Leo. Randall came and untied Leo. Aaron told Leo that if he doesn't fix the technopathy problem, he would die.


  • He is the only person who knows about Ryan's past and the development of his powers.
  • He is the only adult on the Mech-X4 crew.
  • His last name comes from Mendel's Genetic Laws in Biology.


Season 1

Season 2


Disney XD Logo
To view the Leo Mendel gallery, click here.