At some point in time, Marie Laveau sold her soul to Papa Legba in order to acquire immortality; in exchange, he asked Marie for the annual sacrifice of an innocent life at any time of his choosing.
Personality and appearance
Papa Legba is a tall, shadowy Loa, or spirit of Haitian Voodoo, with coal-red eyes, grey-white face paint in the shape of a skull, and long black dreadlocks. He wears a dark overcoat that tapers down to the ground, matched by a hat with small skulls around it, decorated with various bird feathers. His nails are yellowed and long, and he uses them to snort drugs offered to him by those petitioning for his presence. He is mainly seen walking with a cane.
Being the gatekeeper of the spirit world, Papa Legba is always interested in acquiring souls, no matter who they are from. He particularly enjoys making deals with those that are needing of valuable life lessons and negligent of consequences, preying upon their fatal flaws (i.e. greed, vanity) in order to force them under his servitude and, when they fail to uphold their end of a bargain, torment them for eternity after their deaths as punishment for their wickedness. He was willing to make a deal with Fiona Goode for her soul despite her narcissism, cruelty, and murderous behavior, but revoked the deal when he found that she lacked a soul in the first place.
Despite his often antagonistic and somewhat sadistic persona, Papa Legba is an honest and fair individual. He explained clearly and honestly his terms of granting immortality to Fiona when she asked for details. Upon being asked by Queenie about the dynamics of Marie and Delphine's immortality, he explained every meticulous detail of their arrangement, in the process praising Queenie for her sharp mind and powerful magic in having been able to enter and exit the spirit world successfully.
What Papa Legba does with the innocent souls he acquires from his accomplices is unknown. Because these souls have done no injustice, and therefore nothing to warrant damnation in their own personal Hell, it can be assumed that Papa Legba sends them to a lighter afterlife that doesn't warrant eternal torment. When Nan was drowned by Fiona and Marie in a bathtub, he promised to take her to an afterlife where she would find treats for girls "just like her", presumably bringing her to Heaven. Despite Nan having murdered Joan Ramsey, it can be assumed that Papa looks upon the murder of those that have committed sinful acts as being positive; a favoritism demonstrated in that Joan killed both her husband and son before being killed by Nan in retaliation, which Papa would see as a justifiable act.
In order to make a deal with Papa Legba, an individual must have a true desire and intent to see him, and must offer something of value to pique his interest. Being a spirit of life and death, Legba is able to grant wishes to those who request them - including immortality - but these wishes come with a steep price - the willing dispension of one's soul into his possession. After granting their request, the aforementioned individual is from then on in service to him, and must perform any act that he commands them to carry out. Oftentimes, this is the sacrifice of an innocent soul on any day of his choosing, every year. As time passes, he demands worse sacrifices in an attempt to psychologically drive the person into madness for their desires. Reneging on their part of the deal will result in Papa doing the same and reversing their wish, often with dire repercussions.
Papa Legba first appears and awakens a sleeping Marie and demands that she pay his price and reminds her that once a year she must provide a soul for him. He appears again in a flashback as Marie explains to Fiona how she became immortal and how long ago she gave birth to a baby, but Papa Legba wanted her to give up the infant to him, she tried to take back the deal and become mortal again but could not was forced to give him her child. Fiona called Papa and tried to arrange a deal with him for immortality and she agreed to his terms of service, but when she tried to finalize the deal, he says the deal is off because she has 'nothing to sell' saying she has no soul and then disappears. Then after Fiona and Marie drown Nan in the tub he appears and tells them that he won't accept any substitutions and that they must provide an innocent soul, after they try to convice him, he comments that the two of them together are 'big trouble' and then escorts Nan's soul to the afterlife though she comments it is better than being in the coven. 
Queenie later takes up audience with Papa Legba, using voodoo magic to enter the spirit world where she finds herself in Chubby's, where she used to work. Papa Legba appears to her and explains that this is how Queenie perceives Hell, the place where she was treated badly and considered herself worthless. Queenie then inquires over where Marie Laveau is. Papa acknowledges this, then warns Queenie to leave or be stuck in the afterlife forever. After returning to her bedroom, Papa Legba reveals that Marie has been dismembered and scattered by Delphine LaLaurie, and tells Queenie that while Marie lives, so also will Delphine. Queenie notions that because Marie is disembodied, she can no longer pay her service to Papa Legba.
When Delphine finds herself incarcerated in the spirit world, tortured by Marie Laveau, and the latter refuses to butcher Delphine's daughter, Papa Legba appears. He says to Delphine 'welcome to Hell', prompting Marie to question why she is dead. Papa Legba tells her that she could not hold up her end of the bargain, and that he owns her soul. He orders her to 'get back to work'. 
After Fiona dies, Papa Legba appears in her hell, laughing maliciously at her torment. 
- To Fiona Goode: "The deal is off. You have nothing to sell. You have no soul."
- To Queenie: "You are one crafty witch."
- To Delphine in her Hell: "Congratulations, Madame Delphine LaLaurie; you have been granted your sweet release from the world of the mortal. And as punishment for your crimes of murder, torture, passion, fashion, and being an all-around, no-good miserable bitch, you will spend all of eternity here... in my home."
- To Marie and Fiona after killing Nan: "You two, together, big trouble."
- To Fiona Goode: "I don't give a wet donkey's shit about your title. I shine to only one thing; your soul."
- To Queenie in her Hell: "No, darling. Its not the hell... it's your hell. This was the worst time of your life, waiting on people who treated you like the piece of trash you thought you were. No power, no respect, and no future that you could see. Just grease in your hair and the smell of lard in your nose."
- To Queenie: "Took some skills to come down here before you die. Most people be afraid they couldn't get back. It's almost sun up; unless you want to stay here forever, you better hurry and get back. Time... move differently in Hell."
- Despite being named after the Voodoo Loa Papa Legba, this character has more in common with Baron Samedi however Samedi has been used regularly as a character in fiction so the producers of the show likely wanted to use a different name.
- Papa Legba is the first deity to appear in American Horror Story. The second is Scáthach, a minor Celtic goddess.
- See also: Papa Legba/Media
- ↑ Episode: The Magical Delights of Stevie Nicks
- ↑ 2.0 2.1 Episode: Go to Hell
- ↑ Episode: The Seven Wonders