The Binding of Isaac allows you to use eleven playable characters, each with their own attributes. In the realm of the original story of Isaac, they would make no sense taking Isaac’s place, but all of them are references to the Bible with the exception of ??? (henceforth known as Blue Baby) and the Lost. In fact, all of these characters look very similar to the default Isaac skin, meaning that each of these characters could be either Isaac’s imagination or even him wearing a wig or the like. As such, I believe each of these characters represents a trait of Isaac’s personality, and his mother’s intense Christian upbringing of him has caused these traits to become personas of Isaac themselves, similar to a multiple personality disorder or the like. Alternatively, these characters may be Isaac’s imaginary friends, but still represent traits of Isaac’s psyche.
Isaac is, of course, the default character and the only one you don’t have to unlock. He has the most generic stats, and can be seen as the balanced character of the game. Nothing is special about him, but that makes him the most important as the base for the other characters to be judged from.
In terms of story, Isaac is the main character. His namesake shares a similar tale, in which one of his parents attempts to murder him at the request of the Christian God. Isaac was definitely raised in a poor house, with his Christian mother being abusive and forcing her religious beliefs onto him. If the idea that the other characters are simply part of Isaac’s imagination, it would be safe to say that Isaac is well-versed in the Bible. Isaac doesn’t represent any particular part of his own psyche, as he is Isaac.
Magdelene takes her name from the religious figure Mary Magdelene in the Christian faith. She was one of Jesus’s followers, and was present for both Jesus’s crucifixion and resurrection. However, she is related to sin in that she had seven demons cast from her by Jesus, which is referenced in how she is unlocked by having seven hearts.
Magdelene can mean one of two things in terms of Isaac — she is either his tender, kind-hearted side, or representative of his dead sister Maggy. Magdelene is shown to have more generic hearts than any other characters, potentially meaning she is the most human of them all. Isaac would certainly have named his tenderness after the woman in the Bible who closely followed Jesus and supported him throughout his life.
In the Bible, Cain was one of the three sons of Adam and Eve, the first two humans on Earth. He killed his brother in jealously for his better offerings to God, and is considered the first murderer as a result. He is directly related to sin through this murder. Additionally, there is a familiar in the game named Abel, who shoots in the opposite direction of the playable character, so than when you play as Cain the two brothers are faced opposed to one another.
Cain can be seen as Isaac’s jealously as a person. Jealously is taught as a sin in the Christian faith, meaning that Isaac would want to purge this emotion into an entirely new character. The in-game character does not bear many references to this fact, though, and Cain is one of the least fleshed-out characters among the cast. Even his unlock challenge, collect 55 coins, means nothing in the original Bible story.
Judas was one of Jesus’s followers in the Bible, but turned out to be the one who betrayed him to the Sanhedrin in exchange for money. Judas is thought by many to be one of the most sinful characters in the Bible, as his actions doomed Christ to death. Many even associate Judas with the devil, which can be seen in his unlocking criteria of defeating Satan the first time. Judas even starts with three coins, similar to the thirty silver coins he received for betraying Jesus. Additionally, the starting item for Judas is the Book of Belial, which is known for being one of the four books in the Satanic Bible.
The most apparent personality trait of Isaac’s that Judas could possibly represent is betrayal. No other emotion really fits in with what Judas did in the Bible, so Isaac created Judas as the character who would represent this issue.
The Fez means nothing, by the way, just a joke by the creators to give Judas a recognizable item similar to the other characters.
While he is not given an official name in the game, most people reference this character as Blue Baby. He is unlocked by beating Mom’s heart ten times, and is one of two characters to receive their own cutscene. Additionally, Blue Baby is also one of two playable characters who is not a direct reference to the Bible.
Blue Baby is supposed to represent Isaac’s pure soul, as referenced by the fact he only starts with Soul Hearts, as opposed to normal hearts. He is essentially the dead mirror of Isaac, and may even represent Isaac’s fears and doubts about the validity of his own life. Blue Baby even appears as a boss that must be overcome, simialar to Isaac, in order to access a certain route of the game. This route leads to Isaac being able to break free of his home, meaning defeating Blue Baby could represent Isaac striking down his fears of escaping into the real world.
Eve was one of the first two humans on Earth, placed in the Garden of Eden, and was also the first human sinner, making her a prime candidate for Isaac’s personas. Eve must be unlocked by traveling two floors without picking up any hearts, a reference to the fact that outside of Eden Eve and Adam were forced to fend for themselves.
Eve probably represents the blame in Isaac’s life, which he has attempted to pass on to this Eve character. She comes with the Dead Bird and Whore of Babylon items, which while are not direct references to her Biblical story, could show what Isaac thinks of this character.
In the Bible, Samson was a fierce warrior with long hair who had almost limitless strength. However, Samson had a huge flaw that cost him his life — he was incredibly attracted to pretty women and his strength came from his hair, so the one time he sinned he was essentially sentenced to death. Before then, though, Samson was a brave and proud warrior.
Isaac probably associates Samson with his own inner rage, Samson being one of the Biblical characters with the most strength among the list. In the game, Samson is a powerful character with the ability to keep getting stronger through a dungeon, with his weakness actually becoming his strength. Similarly to Cain, however, this connection is not explained much as to why Isaac chose Samson as the herald of his rage.
Azazel was not an actual character in the Bible, but was a term used a few times in many verses such as Leviticus 16:10: “but the goat on which the lot fell for Azazel shall be presented alive before the LORD to make atonement over it, that it may be sent away into the wilderness to Azazel.” The term is Hebrew for scapegoat, and the character seen in Isaac might be acknowledged as a similar concept. Azazel might even be the Isaac seen in the end of Ending 16, as he is a demon who starts with the incredibly powerful Brimstone, a blood laser.
If he is a personality of Isaac’s, Azazel might represent the evil side of Isaac’s conscience. In order to unlock him, you have to take 5 deals with the devil in one playthrough, essentially implying that Azazel is the purely powerful aspect of Isaac’s personality, without any acknowledgement of the good inside.
Lazarus was one of the few figures in the Bible raised from the dead by Jesus himself, and is one of the few playable characters without any real ties to sin. As a character in the game, he doesn’t have too much related to Isaac, but may represent a more fearful side. He has the stereotypical middle part associated with geeks, and is one of the weakest characters in the game at the beginning of a playthrough. However, his unique mechanic of being brought back to life after dying does reference the Biblical story.
Eden is the only character to reference a place instead of a person. Eden was the paradise that Adam and Eve were born into, but eventually had to leave due to the original sin within. Eden is a unique character in the Binding of Isaac, without any set stats or starting items. Instead, every part of the character is randomized upon starting a game, down to the hair on their head. Even their gender is unknown, seeing as the basis for the character was a location.
Eden might represent Isaac’s creative side. The hair can look quite interesting, taking many different forms including a mohawk and a bowl cut. Additionally, in order to play Eden you need an Eden token, potentially being an idea that you need a ticket to get into paradise. Eden could be Isaac being able to forget about his worldly troubles, and just concentrate on being a kid again and playing pretend.
The Lost is fairly unique character, with no reference to the Bible, but similar to Blue Baby in that it is a part of Isaac. The Lost is incredibly hard to unlock, involving dying with certain characters in a certain order against specific enemies. Being such a strange, secretive character, there has been much speculation as to what it is based on. Some players on online forums for the Binding of Isaac have likened it to sperm due to its similar shape, but others have likened it to an already in-game concept of a ghost.
Personally, I support the idea that the Lost is Isaac’s ghost. The same sprite can be seen whenever Isaac (or any of his other counterparts) die, and it would make sense that Isaac’s ghost would not be able to complete challenges as well posthumously. Additionally, the name “The Lost” could reference the lives lost by Isaac when attempting to complete challenges — basically, the failed runs of the Binding of Isaac.