Undertale Guide: Every Character Explained — Story, Lore & Secrets

TL;DR: Frisk is who you play as. Chara is who you named at the start. Flowey is Asriel. Sans knows more than he lets on. Gaster barely exists — on purpose. Every character has a second layer the game only shows you if you’re paying attention.

Undertale has a small cast. You’ll meet most of them in the first hour.

But by the time you finish all three routes, some of these characters will have hit harder than anything in a game three times its size. That’s not an accident. Toby Fox built every single one of them to mean something different depending on what you did.

This guide breaks down each character — who they are, what they want, and what the game hides about them.

Light spoilers throughout. Heavy ones are clearly flagged before they land.

Frisk — The Character You Play As

Frisk is the human child who falls into the Underground at the start of the game. That’s you. That’s the character you’re controlling.

Except — it’s a little more complicated than that.

Frisk doesn’t speak. They don’t have opinions you can read. Their personality is entirely shaped by your choices. Spare every monster and Frisk is kind. Kill everyone and Frisk becomes something else.

One important thing: Frisk is their own person. They’re not just an empty vessel. At the very end of the True Pacifist route, Frisk’s name is finally revealed — and it’s not the name you typed in at the start of the game.

That name belongs to Chara.

Chara — The First Human

Here’s where it gets interesting.

When you start a new game, Undertale asks you to name “the fallen human.” Most players assume they’re naming Frisk. They’re not. They’re naming Chara — the first human child who fell into the Underground long before the events of the game.

Chara was adopted by Toriel and Asgore. They became close with their son, Asriel. They hated humanity. The game never fully explains why — Asriel says even he didn’t know the full reason.

Chara eventually died. Asriel absorbed their soul to cross the barrier and return their body to the surface. The humans attacked. Asriel refused to fight back. He died. And that’s where Flowey comes from.

Is Chara Evil?

This is one of the most debated questions in the entire Undertale community. And the honest answer is: the game leaves it open.

On the Genocide route, Chara appears at the end. They take credit for what happened. They offer to erase the world and move on to the next one. They look directly at you — the player — and wait for your answer.

But here’s the key thing: Chara only shows up when you’ve already done the killing. The game strongly suggests that Chara mirrors your actions. If you kill everyone, Chara is the destroyer. If you spare everyone, Chara is barely present at all.

Whether Chara is a monster or a mirror is something Toby Fox has deliberately left unanswered. Don’t let anyone tell you there’s a definitive answer. There isn’t.

Flowey — The Flower Who Remembers Everything

Flowey is the first character you meet. He seems harmless. He isn’t.

Flowey is Asriel Dreemurr — the prince of the Underground — reborn as a flower after his death. He was brought back to life through one of Alphys’s experiments involving determination. But he came back without a soul. Without empathy. Without the ability to feel anything.

So he tried to fill that emptiness through power. He reset the timeline over and over, killing everyone, befriending everyone, seeing every possible outcome hundreds of times. He got bored of all of it.

By the time you arrive, Flowey is the most dangerous thing in the Underground. He knows more about what’s happened across timelines than anyone else. And he’s the only character — besides Sans — who has any real awareness of what you’re doing.

On the Neutral route, Flowey absorbs the six human souls and becomes Photoshop Flowey. That’s not a boss fight. That’s a nightmare.

On the True Pacifist route, you meet him again as Asriel — his real self. And that’s the heart of the whole game.

Toriel — The Mother Who Stayed

Toriel is the goat-like monster who rescues you in the Ruins. She’s warm, she bakes pie, she wants to protect you.

She’s also the former queen of the Underground. She left Asgore after he declared war on humanity and vowed to kill humans to collect their souls. She couldn’t stop him, so she left — and spent years in the Ruins protecting children who fell in, knowing she couldn’t keep them forever.

Toriel’s boss fight is one of the most emotionally rough moments in the game — especially when you realize she’s not actually trying to hurt you. She’s testing you. She wants to know if you’re strong enough to survive out there on your own.

Spare her. Always spare her.

Sans — The Laziest Character Who Carries the Most Weight

Sans looks like a joke. Puns, ketchup, napping on the job. He’s the comic relief.

Then you get to the Genocide route.

What Does Sans Actually Know?

Sans knows that timelines exist. He knows that something — or someone — has been resetting and restarting the world over and over. He calls it “the anomaly.”

He doesn’t remember specific past timelines the way Flowey does. But he can read your face. He can tell when you’ve done something before. He notices things other characters miss completely.

There’s a hidden room in his workshop in Snowdin. Inside is a strange machine, some blueprints, and a photo of people you don’t recognize with a note that says “don’t forget.” Nobody fully agrees on what this means. It connects to Gaster. It suggests Sans has been doing research no one else in the Underground knows about.

The Promise He Made to Toriel

Before the game starts, Sans and Toriel were pen pals. They passed notes back and forth through a door in the Ruins. She made him promise to protect any human who came through.

That’s why he doesn’t kill you on sight. He made a promise. He hates making promises.

If you betray that trust on the Genocide route, the promise is off. And that’s when you find out what Sans can actually do.

His fight is the hardest in the entire game — not because he has high health, but because he cheats. He attacks during your turn. He uses tricks the game never warned you about. He’s been watching you this whole time, and the fight reflects that.

He has 1 HP. The fight is pure endurance.

Papyrus — The One Who Believes in You

Papyrus is Sans’s brother. He’s loud, dramatic, and obsessed with becoming a member of the Royal Guard. His puzzles in Snowdin are terrible. He thinks they’re incredible.

He’s also one of the most purely good characters in the game.

Even on the Genocide route — after you’ve killed everything in Snowdin — Papyrus spares you immediately in his boss fight. He believes you can still be a good person. He tells you this right before you kill him in one hit.

That moment lands differently depending on how you’ve been playing. That’s the point.

On the Pacifist route, befriending Papyrus is a required step for the True ending. Visit his house after you spare him. Go on the date or the hangout — whichever one you triggered. He’s genuinely one of the best characters in the game.

Undyne — The Hero Who Would Die For Everyone

Undyne is the head of the Royal Guard. She chases you through most of Waterfall trying to kill you. She throws spears.

She’s also fiercely loyal, passionate about everything she does, and completely in love with Alphys — though she’d never admit it easily.

Undyne’s arc across the three routes is one of the sharpest character journeys in the game:

The cooking lesson scene is peak Undertale. Go in knowing nothing about it. It’s worth it.

Alphys — The Scientist With Too Many Secrets

Alphys is the Royal Scientist. She built Mettaton. She’s obsessed with anime. She’s awkward, nervous, and genuinely trying her best.

She’s also hiding something massive.

The True Lab — accessed during the Pacifist route — reveals what Alphys has been covering up. Her experiments with determination went wrong. Monsters who absorbed it couldn’t handle it. They fused together into Amalgamates — creatures that shouldn’t exist.

She never told anyone. She hid them underground and built a fake history of heroism to compensate for the guilt.

Her date sequence and the True Lab are the emotional core of the second half of Undertale. By the end of it, you understand her completely.

For the True Pacifist ending, you need to fully befriend Alphys — deliver Undyne’s letter, go on the date, complete the True Lab. She’s the final piece.

Mettaton — The Star Who Wants Out

Mettaton is a robot built by Alphys. He’s a TV presenter, a quiz host, a news anchor, and a musical performer — all in the space of one area.

He comes across as pure spectacle. But his actual story is quieter than that.

Mettaton is a ghost — specifically Napstablook’s cousin — who wanted a physical body so he could perform. Alphys built him a robot body. He’s been using it to chase fame ever since.

What he actually wants is to reach the surface. To perform for a real audience. He never gets to say this to you directly during the main game — but it’s there if you look.

On the Genocide route, he fights you as Mettaton NEO. A powerful-looking form with no attacks. He dies in one hit. The whole encounter is designed to make you feel terrible.

Asgore — The King Who Made a Terrible Decision

Asgore is the king of the Underground. He declared that he would kill any human who fell in and collect their souls to break the barrier.

He’s also one of the gentlest characters in the game.

Asgore doesn’t want to fight you. He gives you every opportunity to leave before the battle. He waters his garden. He makes tea. He’s been dreading this moment since the day he made that declaration.

He made his vow in a moment of grief — after losing both his children. He couldn’t take it back. Too many monsters believed in it. Too many of them had held on to that hope for too long.

His boss fight is genuinely tragic. You can feel it in the music.

Asriel — The Kid at the Center of Everything

Heavy spoilers below. Read only if you’ve finished the True Pacifist route or don’t mind knowing.

Asriel is Toriel and Asgore’s son. He died long ago when the humans attacked him as he tried to carry Chara’s body to the surface.

He came back as Flowey through Alphys’s experiments. Without a soul, he couldn’t feel anything. Everything you know about Flowey is Asriel trying — and failing — to feel something again.

At the end of the True Pacifist route, he absorbs the six human souls and every monster soul in the Underground. He becomes the final boss. God of Hyperdeath.

He can’t be beaten by damage. The only way to reach him is through the SAVE option — calling out to your friends, one by one, until their voices break through his power.

When he finally lets go — when he remembers who he was — it’s the most affecting moment in the game. Probably one of the most affecting moments in any game.

After the fight, find him in the flower field before you leave. He has one last thing to say. Don’t skip it.

W.D. Gaster — The One Who Barely Exists

Gaster is the biggest mystery in Undertale. And the game gives you almost nothing on purpose.

W.D. Gaster was the Royal Scientist before Alphys. He fell into his own creation — likely the CORE — and was scattered across time and space. Most monsters don’t remember him. The ones who do are unstable.

You can only encounter Gaster through the Fun Value system — a hidden number assigned to your save file on each reset. If it lands on the right values, Gaster-related events appear: strange followers, a sound test room, a fake hallway in Waterfall, a mysterious figure behind a grey door.

None of these events tell you what happened to him directly. They suggest. They hint. They leave you with more questions.

The connection between Gaster and Sans is one of the most discussed mysteries in the game. Their attacks share the same assets in the game files. Sans’s machine in his workshop looks like it could be related to Gaster’s experiments. The River Person drops cryptic warnings about “the man from the other world.”

None of it is confirmed. All of it is deliberate.

Explore the Full Guide

This is one part of a five-post Undertale guide. Here’s where the rest takes you.

Undertale Guide: Everything You Need to Know Before You Start → New to Undertale? Start here. Routes explained, how long it takes, and beginner tips that matter.

Undertale Guide: Full Walkthrough — Every Area, Boss & Route → Step-by-step through every area. All three routes covered. Includes boss tips and how to unlock the True Pacifist ending.

Frequently Asked Questions

Who do you name at the start of Undertale — Frisk or Chara? You name Chara — the first human who fell into the Underground long before the game begins. Frisk is the character you actually play as, and their name isn’t revealed until the end of the True Pacifist route.

Is Chara the villain of Undertale? The game intentionally leaves this open. Chara only appears as a destructive force on the Genocide route — a route that requires you to kill everyone first. Many players interpret Chara as a reflection of the player’s own choices rather than an independent villain.

Does Sans remember past playthroughs? No — not in the way Flowey does. Sans knows that timelines exist and can sense when something has happened before based on your behaviour and expressions. But he doesn’t have clear memories of specific past runs. Flowey is the only character who fully retains memories across resets.

Why does Papyrus spare you on the Genocide route? Because Papyrus genuinely believes every person is capable of being good. Even after you’ve killed everything in Snowdin, he spares you immediately. He thinks you can still turn around. It’s one of the most deliberate and heartbreaking moments in the game.

What is the connection between Gaster and Sans? The game hints at a connection without confirming one. They share visual assets in the game files. Sans has an unexplained machine in his workshop. The River Person warns about “the man from the other world.” Toby Fox has never confirmed the exact relationship, and that ambiguity is intentional.

Do you have to befriend all the characters for the True Pacifist ending? You specifically need to befriend Papyrus, Undyne, and Alphys. Toriel and Sans are befriended through the natural flow of the Pacifist route. Missing any of the three required friendships means the True Pacifist ending won’t trigger.