The relationship between the Upgraded Original Vampire Marcel Gerard and the vampire Thierry Vanchure. The two were best friends, having known each other since the 1940s, when Marcel found Thierry dying of a war wound outside of a VA hospital and turned him into a vampire to save him. Marcel relied on Thierry as his most trusted confidant. However, when Thierry inadvertently killed a fellow vampire, breaking Marcel's number one rule, Marcel sentenced Thierry in the Garden for one hundred years, not knowing that Niklaus Mikaelson had tricked Thierry into killing him. After this betrayal, Thierry was willing to go against Marcel and Klaus by allying with Rebekah, but their plans eventually fell through.
After Thierry was pardoned by Klaus and released from the Garden, he remained resentful toward Marcel and even left the vampire community of the French Quarter in favor of laying low in nearby Algiers. This estrangement was ultimately short-lived, though, and ended when Thierry and Marcel reconciled and worked together to take down Klaus and regain control of the Quarter. Unfortunately for the two vampires, Marcel's plans to destabilize the newly-enacted truce between the five factions of New Orleans caused the ire of the Mikaelson family, and Thierry was killed by Elijah Mikaelson in order to get payback against Marcel for his actions, much to Marcel's devastation. After Thierry's death, Marcel vowed to get vengeance against Klaus and Elijah once and for all.
Throughout The Originals SeriesTangled Up In Blue, Thierry and Marcel discussed business at the compound while they prepared for the party. Thierry informed Marcel that he and the other vampires were beginning to worry about their community with the return of Klaus and Rebekah Mikaelson to New Orleans. Klaus, who was eavesdropping on their conversation, joined them in the room and made a joke about how he had bitten Thierry before saying he thought they were "at bygones." Thierry became angry and remarked to Marcel that he had given Klaus full run of the compound, and Klaus reminded him that he not only built the house but also the town. When Klaus then asked Marcel if he could get Elijah (whose daggered body was being held by Marcel and Davina) back at Rebekah's request, Thierry became even more worried.
Thierry turned to Marcel and asked, "We're not gonna have three Originals walking around town, are we? Half our guys think the sister killed the nightwalkers". Klaus then became angry at Thierry for accusing his sister of the murders, forcing Marcel to step between them to mediate before they get into another fight. Marcel reminded Thierry that Klaus was a guest of his, and then reminded Klaus that Thierry was right, and that if he gave Elijah back, it would make the other vampires start to question who was in charge. Later, when Klaus and Marcel were talking privately, Marcel told him about how he and Thierry met in the 1940s when he saved him from dying from a war wound outside of the VA hospital and informed Klaus that Thierry was his right-hand man. Klaus ultimately used this information to manipulate Thierry into staking and killing one of Marcel's nightwalkers after he went after Thierry's girlfriend, the witch Katie. Because killing a fellow vampire breaks Marcel's number one rule, Marcel sentenced Thierry to one hundred years in the Garden.
In Fruit of the Poisoned Tree, Marcel visited Thierry in the Garden and confessed that he was the only person he could actually trust. After temporarily freeing Thierry from his "cell" and giving him some blood, Marcel asked him for more details of what happened the night that he killed the nightwalker, Max. Thierry explained that even though Marcel ordered them to roust at the Cauldron, he didn't say to kill, and so he tried to intervene when Max went straight for Katie and tried to feed on her. When he wouldn't stop, Thierry killed him, and after thinking about it during his imprisonment, he theorized that Max may have been compelled by one of the Originals. Marcel assured him that it was impossible because all of his men were on vervain, but Thierry reminded him that Max went missing for a few days prior to the rousting and suggested that maybe Klaus bled him dry of vervain so he could be compelled.
In Le Grand Guignol, Thierry, who had moved to the neighborhood across the river from the French Quarter, met at the docks with Rebekah and Marcel, who were on the run from Klaus after he had learned of their betrayal in 1919. They begged Thierry for his help in killing the three remaining resurrected witches who had taken the life force meant to resurrect the Harvest girls so they could get Davina back and get her help in cloaking them from Klaus. Thierry reluctantly agreed and arranged for a meeting with Bastianna Natale, Genevieve, and Céleste Dubois, although only Bastianna and Genevieve showed up. Thierry began the meeting as though he wanted to form an alliance with them against the Originals, but then he, Marcel, and Rebekah attacked them together. Marcel was able to kill Bastianna, but Genevieve got away, forcing Rebekah and Marcel to go get Davina's body and hope that they killed the correct witch.
In The Big Uneasy, Marcel and Thierry planned on disrupting the witches' celebration of La Fête de Bénédictions in the French Quarter. They compelled a group of drummers to show up to the after party and slice their wrists open in order to tempt the vampires in attendance into feeding on them and ruining their peace treaty with the other supernatural and human factions. Their plan worked as intended, and the vampires were so overcome with bloodlust that they attacked and killed all the drummers and many of the human attendees of the party. However, Elijah realized who had orchestrated the scheme and tracked Thierry and Marcel down to Marcel's loft across the river, where he killed Thierry as a punishment for Marcel, knowing that he couldn't kill Marcel without incurring Klaus' wrath and that Thierry's death would ultimately be more painful for Marcel. That night, Marcel held an impromptu funeral outside of his apartment with Diego and several other vampire friends, where they toasted to Thierry's life, doused him in alcohol, and set him on fire. While saying his goodbyes, Marcel vowed to avenge Thierry's death.
In The Battle of New Orleans, Marcel kidnapped Klaus and Elijah's allies, the werewolves Jackson Kenner and Oliver to torture them for information on what Klaus was planning. When Klaus and Elijah arrived to rescue them at Thierry's warehouse by the docks, Klaus found crates full of explosives that Marcel had left as a trap. In the last crate, Marcel left a note that read, "This is for Thierry," revealing that his intention was getting back at the Mikaelsons for Thierry's death.
In Rebirth, Marcel mentioned Thierry while talking with his fellow vampire Josh. As the two listened to a jazz record on Marcel's gramophone player, Marcel informed Josh that it was the only album his friend Thierry had recorded of himself playing the trumpet and used it as motivation for them to keep fighting for their homes in the French Quarter and New Orleans in general.
- Marcel trusted Thierry more than anyone.
- Klaus gave Marcel permission to free Thierry from the Garden.
- They were no longer best friends after Marcel imprisoned him in the Garden, but they did ally together against Klaus before Thierry died.
- Marcel owns the one and only vinyl record Thierry ever recorded of himself playing jazz music on the trumpet, something Marcel said he only could have done in New Orleans.