Diego was a major recurring character of The Originals. Diego was a vampire who was sired by Marcel Gerard. He was one of the members of Marcel's inner circle who gained daylight rings upon entry, and functioned as a member of Marcel's army. He was loyal to Marcel and many of his fellow high-ranking vampires, including Thierry Vanchure. Just like Thierry, Diego did not like or trust the Original vampires.
As of Moon Over Bourbon Street, Diego had become the leader of the vampires remaining in New Orleans after Elijah revoked their privileges in the Mikaelson compound. However, after the death of his friend Thierry, he agrees to join Marcel in his plan to overthrow the Originals from their place of power in the city.
Diego is mortally injured by the Guerrera werewolves after he and his vampires confront the Originals under Marcel's leadership. Although Marcel tries to find a way to save his friends from the bite of the werewolf, Diego and the other surviving vampires are killed by the resurrected Mikael, the vampire who hunts vampires.
According to Diego, he and his family were attacked by werewolves, and he watched his sister die in front of him from the wounds she sustained in the attack. Diego only survived because Marcel found him and turned him into a vampire before he could die naturally. From then on, Diego felt an intense hatred toward werewolves.
In The Originals, Diego seemed to be one of Marcel's closest associates, as Marcel came to his rescue when Klaus had lashed out at him. He stated that he only answered to Marcel, and his loyalty to Marcel was so strong that he dared to talk back to Klaus of all people, after Klaus approached him and demanded Marcel's whereabouts. Klaus was so angered by Diego's disrespectful behavior that he grabbed him in a choke-hold until Marcel finally arrived and stepped in to break up their confrontation, insisting to Klaus that Diego was just looking out for him.
In Always and Forever, Diego was often seen with Thierry doing Marcel's bidding. He was shown to be very loyal to Marcel and followed all of his orders.
In House of the Rising Son, Diego was seen alongside Marcel and Thierry. During the party Marcel threw at the Abattoir, Diego was seen watching over the party-goers and feeding various guests, all of whom were healed later on with vampire blood. The next day, Diego and Thierry were present when dealing with Tina and Josh after they were inadvertently killed after being healed with vampire blood at the party. Marcel ordered the two to dispose of Tina's body in cold storage after he killed her, which they obliged.
Diego appeared in Tangled Up In Blue and was seen the night Sophie, Rebekah, and Klaus attempted to stop Marcel, who was being backed up by the young witch Davina. When he, Thierry and other fellow vampires under Marcel's leadership went rousting through the Cauldron on Marcel's orders, Diego witness Thierry kill a vampire named Max, who, unbeknownst to them, was compelled to kill Thierry's girlfriend, Katie. Diego was shocked by this turn of events, and was the vampire who broke the news to Marcel that Thierry broke his most important rule. He also accompanied Marcel when he questioned Thierry on his actions against Max.
In Girl in New Orleans, Diego was seen feasting on a victim in a bar when Rebekah paid him a visit. She asked him about Marcel's current love life, but Diego initially rejected her attempts to gain information. Eventually, Rebekah managed to convince Diego to admit that Marcel is a busy man, so if he had a girl he was seeing, she would likely be close to the Quarter. Later, Diego was blamed by Marcel for losing Davina during the Dauphine Street Music Festival. Diego then instigated a heated argument with Marcel about his treatment toward Thierry, which resulted in Marcel snapping his neck as punishment for his insubordination.
In The River in Reverse, Diego was seen on Marcel's side of the growing fight between Marcel and Klaus at the compound. During the intense battle, Diego managed to get in a few hits against Klaus, though he witnessed the deaths of many of his fellow vampires around him. He was knocked down at numerous points of the battle, but managed to survive once Marcel took Klaus' coin and pledged his loyalty to him to ensure that none of his community were slaughtered. Diego was extremely angry at Marcel for surrendering, and was seen drinking straight from a bottle of liquor before using it to douse the bodies of his fallen friends so he could incinerate their remains.
InReigning Pain in New Orleans, Diego was seen at the dinner Klaus hosted alongside the other vampires, which Klaus hoped would help reunify their community and win them over. Ultimately, Diego, after talking to Marcel, agreed to serve Klaus until they could find a way to get control back, though Diego was not pleased to do so. Later, Klaus sent Diego to lead the vampires on a werewolf hunt in the Bayou to try to reassure them that Klaus had no intention of siring more hybrids with his daughter's blood. Hayley tried to sneak out of the compound to warn her family in the Bayou and ran into Diego, who rudely asked her if she was planning on going somewhere. Fortunately, Elijah and Rebekah arrived just in time to break Hayley out of the house, and snapped Diego's neck before he could interfere. Hayley was more concerned about the werewolves, though, and insisted that Elijah and Rebekah go to the Bayou to warn them of the incoming vampire attack. When Diego and the vampires arrived to go hunting, Elijah and Rebekah stopped them and sent them away, though Diego and his men did circle back around in an attempt to do what Klaus ordered one last time before being threatened into leaving.
In Dance Back from the Grave, Diego and the other daywalkers congregated in the courtyard, waiting for Klaus, when Marcel joined them and asked what their meeting was about. Klaus then arrived with Thierry Vanchure, Diego's best friend and revealed that he had pardoned Thierry for his crime of killing a vampire. Diego and the other daywalkers welcomed Thierry with open arms as Klaus then explained to Diego and the others that now that since Davina had died and the Harvest had failed, the witches would soon lose their magical powers. He insisted that they needed to keep the witches on their toes in the meantime, and offered to allow Diego lead a rousting in the Cauldron. When Diego and the vampires did as they were told, they found the bodies of two vampires who had been desiccated and left to lay in a ritualistic circle, and called the rest of the vampires (including Klaus and Marcel) to come see it for themselves. Marcel, recognizing the symbol as the mark of a powerful witch he knew in 1919, informed the vampires that they would be best served staying at the Abattoir and not seeking out whoever had been killing the vampires. Klaus, furious, insisted that whoever was responsible needed to pay for what they did, but the other vampires looked hesitant to get involved.
Later at the Abattoir, Klaus and Elijah discussed which witch was responsible for killing the nightwalkers with magic, and discussed the witch they knew who practiced that form of magic in the late 1910s, Papa Tunde. Klaus then instructed Diego to find whoever killed them and put their heads on pikes, but Diego replied that the vampires were all scared and freaked out by what had happened, as witches hadn't had any power against the vampires in decades. Annoyed and frustrated, Klaus left to deal with it himself. After Papa Tunde attempted to kill Klaus and Marcel at Rousseau's, Klaus gave a speech to the vampire community of New Orleans and informed them that they were under attack. He also explained that since he needed soldiers in the war against the witches, they needed to decide if they were going to stand with him or leave the French Quarter. Diego was among the vampires who decided to stay with Klaus and a reluctant Marcel.
In Crescent City, Diego called Klaus after he and other daywalkers found that Papa Tunde's body had been brought to them at the Abattoir by the witches. Later that day after the witches took Klaus down with Papa Tunde's Blade, Diego told Marcel that they looked all over the French Quarter, but they couldn't find him. Diego then saw Elijah come in watched as he tossed away two vampires and demanded that they all help him find his siblings and kill the witches who took them.
In Moon Over Bourbon Street, since losing their place as the dominant faction of New Orleans, the vampires had been fighting to reclaim their position under Diego's leadership, attacking witches and even the members of the human faction who tried to end the bloodshed. Elijah, fed up with the escalating conflict and Klaus's refusal to do anything about it, called a peace summit between the vampires (led by Diego) and the witches (led by Genevieve) at St. Anne's Church, under the supervision of both himself and Father Kieran, each of them representing the Originals and the humans. However, the mere question of setting boundaries for the different factions caused the talks to break down into a shouting match between the vampires and the witches. When Elijah finally managed to impose order, Hayley arrived, furious about the fact that the werewolves had been excluded from negotiations.At this point, the talks broke down again, and the different factions walked out. Later, Diego attended the party held by Elijah at The Abattoir to try to unite the factions to finally hammer out a peace treaty. Diego was approached by Elijah at the party and told to be respectful to their guests, so Diego admitted that he hated werewolves because they had killed his sister and would have killed him as well had Marcel not turned him into a vampire first. Hostilities were quickly exchanged again at the party between Diego and Oliver, a werewolf, and eventually descended into a physical fight. Elijah intervened and pulled Diego off Oliver, ultimately getting into an altercation with Oliver until he saw that Jackson had pinned Diego against a wall and held a stake to his heart, threatening to kill Diego if Elijah didn't let go of Oliver. Hayley then gave a speech to the party-goers that finally motivated them all to sign a peace treaty and begin respecting each other to end their everlasting cycle of violence between factions. That night, the representatives of the five factions all mixed their blood in a well and used it to sign their treaty; the signers were Elijah and Klaus (representing the Originals), Diego (representing the vampires), Hayley (representing the werewolves), Francesca (representing the humans) and Genevieve (representing the witches).
In The Big Uneasy, Diego was seen talking to Elijah, who informed him that since he signed the treaty, it would be best if they attended the Feast of the Blessings in honor of the witches to show solidarity. Diego was later confronted by Marcel and Thierry, who hoped he would join them in their plan to retake New Orleans, but Diego rejected their proposal and insisted that he picked the winning team, citing the fact that while Elijah may not be the nicest person, at least with him he knew where he stood. Diego was one of the many vampires who were baited into attacking a group of compelled drummers who crashed the festival; the drummers were humans compelled to slit their wrists in the middle of the party, which triggered the vampires' blood cravings and caused them to attack the drummers and several other humans and witches in attendance, shattering the fragile peace treaty. After Diego learned of Thierry's death at Elijah's hands, Diego attended Thierry's funeral and officially agreed to join Marcel's cause against the Originals.
In An Unblinking Death, Diego was hanging out in the Pit when Hayley found him and demanded he give her information about the bombing at the Bayou. Diego rudely retorted that she had a lot of nerve to be showing up on their territory, so Hayley shoved him against a wall and stabs a stake into his chest, barely missing his heart. Diego then confessed that Marcel was living in an apartment across the river and told her where she could find him. He was later seen meeting with Marcel and discussing their plans.
In The Battle of New Orleans, he participated in the fight against Elijah and Klaus in the courtyard of the Mikaelson compound. Unfortunately, he was seriously injured, and hid on the sidelines until he was able to heal and rejoin the fight. After he saw Elijah get knocked down and attacked by the newly-triggered Guerrera werewolves, who had stolen the moonlight rings Klaus had hired Genevieve to create, he tried desperately to warn his fellow vampires so they could get away. Unfortunately, he and the rest of the vampires were all bitten and left for dead in the courtyard.
In From a Cradle to a Grave, Diego was among the majority of the vampires who were suffering from werewolf bites in the Battle of New Orleans. While he was waiting for Marcel to return with Klaus' blood so he could be healed, he was attacked and fed on by Mikael until he finally died. Marcel later returned and found his body and nearly broke into tears at the sight of his dead friend.
Little was known about Diego's personality, but from what has been seen, he was incredibly loyal to Marcel. He also seemed to be very close friends with Thierry Vanchure, as he was indignant towards Marcel on Thierry's behalf when Marcel sent him to the Garden. He apparently had an intense hatred for werewolves, as his entire human family faced tragedy at their hands before he was turned into a vampire by Marcel. His transition into being a vampire seemed to only exaggerate this hatred, as vampires and werewolves have been natural enemies for over a millenia.
Diego seemed to be loyal to Marcel and was a close friend and associate of his. He was loyal enough that Marcel gave him a daylight ring, which are only reserved for his inner circle, and he was willing to stand up to Klaus for him. However, he seemed to be angered by Marcel's treatment of Thierry after he was sent to the Garden. After Marcel lost his battle with Klaus in The River in Reverseand picked up the coin, Diego lost respect in Marcel, as he believed Marcel only picked the coin to save himself. In The Big Uneasy, Diego rejoined Marcel's team after coming to the conclusion that they must take the city back from the Mikaelson's control.
Based on Diego's anger at Thierry's sentence and the anger he expressed towards Marcel, it can be presumed that the two of them were close. He was also extremely saddened when he was killed, drinking for him at his impromptu funeral.
Diego did not seem to harbor any true ill will against the Mikaelson Family (though he, like many vampires in the Quarter, seemed to distrust them and often acted arrogantly around them). However, he rarely showed them any outward support unless it was to help solidify his own role as a leader of the vampires. Though he later became compliant to Klaus and Elijah's rule, he expressed a desire to see them leave New Orleans on several occasions.
Eka Darville, who played Diego, also starred together with Adelaide Kane in Power Rangers RPM, as Hero and Villainess, respectively. Adelaide played Cora, a werewolf in TV show Teen Wolf, continuing the rivalry between their characters, as they each played a vampire and werewolf, respectively.
It was revealed by Diego that his whole family was slaughtered by werewolves in his youth, and he watched his sister die of blood loss. He also confessed that he would have died as well, if he were not saved by Marcel.
Though Diego remained loyal to Marcel for the majority of his time in the series, it was shown that he would choose to save himself first if it came down to it.
Since the Other Side has been destroyed, he most likely found peace or was sucked into oblivion.