- “Don't worry, I have a few tricks up my sleeves.”
- ―Mateo to Naomi
Seventeen-year-old Mateo, as the grandson of Alacazar, and a wizard-in-training, is very interested in all things magical, be they spells, creatures or items. He is constantly seen trying to perfect his spells, yet sometimes his self-doubt and overly cautious nature can keep him from doing so. Yet if Elena and/or friends need him to, he will put all his fears aside and protect them, sometimes whether they want him to or not, with his magic. He can be clumsy and fumble up his spells from time to time as well. However after his friends help him reclaim the Codex Maru, and Elena shows her belief in his abilities, he gains a greater sense of self-worth and proves to be a powerful Royal Wizard, defeating Fiero in a duel.
Mateo has a slim figure with tan skin, brown hair, and hazel eyes. He typically wears a teal vest with a white undershirt, khaki pants, brown boots, and a red neckerchief. In his wizard robes, he wears a long dark red wizard robe.
Mateo first appears when Princess Sofia of Enchancia arrives at his house. He overhears Sofia talking to his mother Rafa about summoning Alacazar's chanul. Mateo walks up to her and questions her about her magical knowledge. Sofia revealed that Alacazar sent her. Hearing this, Mateo deduces that the necklace Sofia's wearing is the Amulet of Avalor and takes Sofia down to his workshop. Once there, Mateo reveals that he's been training himself to become a wizard in secret using Alacazar's old things because Shuriki outlawed magic when she took over. He then summons Alacazar's chanul: Zuzo. Zuzo tells them that, in order to free Elena, Sofia has to wrap the Amulet around Shuriki's wand and put both on the Crown of Aziluna. When Sofia decides to get Shuriki's wand by dancing with Shuriki, Mateo is doubtful the plan will work since Shuriki outlawed dancing when she took over but goes with her back to Avalor Palace. When Sofia comes back with the wand, Mateo is impressed. Together, they fly to the Temple of Aziluna where Sofia does as Zuzo instructed and frees Elena. Mateo introduces himself to Elena and together they fly back to Avalor Palace. After Elena fails to defeat Shuriki on her own, they go back to Mateo's house where Rafa gives them the spell that will free Elena's family. After Mateo frees Elena's family, he then helps her defeat Shuriki and free Avalor.
Mateo first appears in "First Day of Rule". He first appears when Elena shows up at his house with his friend Naomi Turner. They tell him that Elena's sister was abducted by ship thieves and, thanks to one of the books of his grandfather, Alacazar, he identifies the thieves as Noblins. They succeed in rescuing Isabel and later Mateo watches Elena select Naomi to join the Grand Council of Avalor.
In "Spellbound", Elena selects Mateo to fill his grandfather's robes as Avalor's new Royal Wizard. At first, Mateo doesn't believe he's up to the task, mostly because most people don't believe in him but after he obtains the Codex Maru and defeats Alacazar's old enemy, Fiero he proves especially to himself that he was a good hire.
In "The Scepter of Light", he attended the solar eclipse with the Kingdom of Avalor, but Orizaba the Moth Fairy returns to bring eternal night to Avalor using the Eye of Midnight. Mateo goes off to pursue her with Elena not far behind. When she uses her scepter it drains her energy away. Worried, Mateo carried Elena back to the palace to discover that using it repeatedly drains the user's energy and is one of the downsides of the scepter. After Orizaba has been defeated, Elena asks him for help on learning how to use it without passing out.
In "Wizard-in-Training", it has shown that Mateo has grown in his confidence as a wizard and gains an apprentice named Olivia. At first, he has a little trouble teaching but soon learns that he has to guide her every step of the way and admits to himself that he still has a lot to learn.
Mateo continues to aid Elena as Royal Wizard after learning of Victor and Carla Delgado having returned to seek revenge for their earlier defeat. When he learns that they are heading to the abandoned capital of Tepet Muul to retrieve the Jewel of Maru, he and Elena, despite it being Dia de Los Muertos, set off in pursuit of them. He finds the Delgados, but is overpowered and loses his tamberitia to Victor. He later retrieves it with Elena's help and returns to the capital, realizing they missed the celebration, but Elena knows she'll see her parents again next year.
Later, he works on a Reversal Potion that he intends to use to restore Fiero to flesh and blood. However, he is unaware that the person he explains this to, Rita Perez, is really Carla Delgado in disguise, who passes this information back to Shuriki, who makes plans to acquire the potion for herself to revive Fiero and recruit him to her cause to get revenge on Elena and conquer Avalor again.
Shuriki gets her hands on the potion once Carla is able to swipe the key from Mateo's lab right off his neck. It is only later when Mateo discovers his lab ransacked from Carla's earlier search for the Reversal Potion that he is shocked when Fiero, fully revived, appears and attacks him to try and take the Codex Maru. Mateo manages to save the book, leaving Fiero to escape with only a few blank pages. Mateo later arrives in time to save Elena from Shuriki by passing her the Scepter of Light to counter Shuriki's wand and protect her from Fiero. After Elena shatters Shuriki's new wand and Fiero provides a distraction to allow the villains to escape, Mateo gives pursuit on horseback with Gabe, Elena, and Naomi, but lose sight of Shuriki, Fiero, and the Delgados. However, Elena has Gabe summon the Royal Guard to hunt Shuriki and her crew down as they return to Avalor City and the palace.
In the episode that follows, as Elena is told to stay in the palace for her own protection, Mateo has managed to complete his Shape-shifting Potion to turn himself into a Jaquin. After running into Gabe and revealing the potion to him, Gabe joins Mateo and Elena as they head to attend Luna's birthday party with many other Jaquins, including Chief Zephyr. When Elena notices Zephyr leave with Cruz, she and Mateo pursue him to Commander's Rock. Finding nothing of interest there, Elena and Mateo return to the others, only for Cruz to arrive afterward and frame Elena, Gabe, and Mateo for Zephyr's disappearance. Believing him due to their friendship with him, Migs, Luna, and Skylar lock them up, but Elena manages to convince Mingo, Zoom, and Estrella to let them out. After traveling to Commander's Rock and letting Zephyr out, Mateo and Elena pursue Cruz, but Mateo gets snagged in some vines. He later catches up as Elena and Zephyr have captured Cruz, and Gabe, Migs, Luna, and Skylar see to his imprisonment. Back at the castle, Elena asks Mateo about the missing pages from the back of the Codex Maru that Fiero stole, and using the Scepter of Light, they learn of its dark counterpart, the Scepter of Night, and the riddles left behind by Mateo's grandfather Alacazar, that lead to the pieces.
Following the riddles, and joined by Naomi, they travel to the abandoned capital of Tepet Muul to find the first piece. However, Mateo is blinded by pride, thinking that if they get the scepter first, he could become as powerful as his grandfather, maybe even surpass him. However, he ends up in the wrong pyramid at first, and then his pride leads to where he leads Fiero and Victor Delgado to the first piece, leaving him demoralized at his mistake. A pep talk from Elena manages to cheer him up, and he is able to help stop Fiero and Victor from escaping with the piece by saving Naomi, while Elena gets the piece and forces the villains to retreat without it. After Mateo apologizes to Naomi, Gabe, and the Jaquins for his screw-up, they regroup to decipher Alacazar's riddle that leads to the second piece, knowing that Shuriki and her team are heading for it as well.
However, once at the second piece's location in Vallaestrella, the decision is made to have Mateo and Gabe return to Avalor on Migs and Dulce with the first piece while Elena and Naomi get the second and third pieces. However, en route back, Mateo and Gabe are ambushed by the Delgados, now full-fledged Malvagos on Shuriki's order to Fiero, and lose the Scepter of Night's Staff to Victor and Carla. When they return to tell Elena and Naomi, they learn that Shuriki and Fiero got the Mount and Jewel due to Elena's own fault, letting her lust for revenge for Raul and Lucia cloud her judgement so Shuriki has all three pieces now. Luckily, Quita Moz arrives to take Elena to train to unlock the full power of her Scepter of Light, and Mateo sees her off with Gabe, Naomi, and the Jaquins as Elena departs with Quita Moz.
By Season Three, Mateo and Elena decide that it might be time for Mateo to reunite with his grandfather, so they contact Princess Sofia in Enchancia, asking that she send The Lost Princess of Avalor back home to Avalor. Sofia agrees, and once the book is returned to them, Mateo reunites with Alacazar, only to learn that the spell that Alacazar cast to turn him into the book is wearing off. When the book disintegrates, he'll die and go to the Spirit World. Not wanting that to happen, Mateo works with his grandfather to concoct a potion that saves Alacazar, but tragically, he sacrifices himself to protect Mateo from Ash Delgado and a now fully evil Esteban, though his sacrifice allows Mateo and Elena to get the stolen Scepter of Light back from them.
Mateo is then asked by Elena to train the best of her Royal Guards to use magic to fight Ash and Esteban when they return, and though he has Elena and Naomi take Doña Paloma with them to find what he needs to make more tamberitias, he soon has problems of his own when Gabe loses patience with the training, and a protege wizard makes a mess of Avalor Palace that Gabe and his guards can't fix with their inadequate magic training. Mateo is able to set things right before Elena and Naomi return with what he needed and noticed anything.
- Mateo's Tamborita is inspired by the drums used by the Mapuche "Machi" (shaman) in Chile. His spells have Mayan glyphs integrated into them.
- Mateo and Carla might possibly like each other.