Asriel Dreemurr

Asriel Dreemurr (typically /ˈæz.ɹiː.əl ˈdʒɹiː.məɹ/) is the biological child of Toriel and Asgore, as well as the adoptive brother of the First Human. He is Flowey's former self, prince of the Underground, and the final boss of the True Pacifist route.

Appearance
Asriel has a similar appearance to his parents, with long ears, a snout, and visible fangs. In his initial form, he wears a green long-sleeved shirt with yellow stripes, and black pants.

God of Hyperdeath
This form is named directly in the game, where the "Check" option labels Asriel as "the absolute GOD of Hyperdeath!" in this form. The sclera of Asriel's eyes becomes black, his fangs become longer, and he grows a pair of horns. In this form, he wears a long dark robe with white sleeves and the Delta Rune on the front, similar to Toriel's although with a large collar and shoulder pads. He also appears to be wearing a locket similar to the Heart Locket.

Angel of Death
While this form is not directly named, it strongly resembles the Delta Rune, which resembles an "Angel of Death" in a prophecy in the Underground. In this form, his body becomes more geometric, his horns longer and his teeth sharper. He grows a pair of wings that continuously change color, and his lower body becomes sharp and heart-shaped.

Personality
Before his death, Asriel was known to be a docile, unadventurous and loving child who loved jokes. After being brought to life again without a SOUL as Flowey, however, he became incapable of feeling joy, leaving him bored and resentful. After temporarily regaining his compassion, he profusely apologizes for his actions to Frisk, feeling bad as he became aware of how wrong his actions were.

Main Story
Before the events of Undertale, Asriel found the first human that fell into the Underground, who became his adoptive sibling and best friend. When the human died, their last wish was to see the Golden Flowers of their village, on the Surface. Asriel absorbed their soul and carried their body across the barrier to their village, whose inhabitants assumed Asriel had killed the human and attacked him. Asriel, lethally wounded, returned to the Underground where he died. Once deceased, his dust spread across the garden, leaving his essence on it. Later, Alphys, as part of her experiments, injected determination on the first golden flower that bloomed in that garden ever since. This injection brought the flower to life; with the flower as a vessel for his essence, Asriel was reborn into Flowey, although he had no SOUL in this state. Unable to feel love or joy, Flowey took his own life. However, through the determination that Alphys had injected, Flowey obtained the power to SAVE, and Flowey found himself returned to where he was first brought to life. Using that power, Flowey first decided to help the Underground, but became bored, and began killing monsters. After seeing and doing everything he could, he became apathetic.

Name Anagrams
Some people have found out certain "anagrams" for "Asriel Dreemurr". An anagram is a word/phrase/etc. made by rearranging the letters into different places, hence "unscrambling words". For example, "ocean" is an anagram for "canoe" and "secure" is an anagram for "rescue".

Serial Murderer
This one is a really clever anagram, and would be a bit hard to discover. This could mean something about Asriel. Did Asriel murder someone? Maybe it was a different situation? Nobody knows what this could mean for now.

Dreamier Rulers
This one is a bit more harder in a way to find, since you'd have to rearrange the letters in both the first one and the last one, but Serial Murderer seems a bit more accurate. Dreamier Rulers sounds a lot like Asriel, and his name "anagramed" to Dreamier Rulers may have just been for fun.

Neutral Route
When the protagonist falls into the Underground, their determination outweighs Flowey's, taking away his ability to SAVE. Flowey first tells the protagonist that in this world, "it's kill or be killed", and tries to kill them in an attempt to steal their SOUL, but is stopped by Toriel. He appears again at the end of the Ruins after fighting Toriel.

Later on, when the protagonist falls into the Garbage Dump, Asriel appears in an old memory of the Fallen Child's.

True Pacifist Route
In the True Lab, it is discovered that the first human, along with Asriel plotted to get to the surface and collect six more human souls to break the barrier, by having the human poison themself with buttercup flowers and having Asriel absorb their soul. Though while the human was on their deathbed, Asriel informed them he did not think it was a good plan anymore and was having doubts, ultimately leading to him backing out of the plan in the future.

After restoring the elevator's power, the protagonist receives a phone call from what is believed to be Asriel, mistaking the protagonist for the first human. Asriel appears again as Flowey when the protagonist and their friends come together after they try to fight with Asgore. A vine from Photoshop Flowey appears, and it tangles and traps their friends. More monsters show up, encouraging the protagonist to continue fighting. Flowey absorbs the SOULs of all monsters that showed up to support the protagonist in the Underground, as well as the six human souls, and transforms back into Asriel. Asriel tells the protagonist that he does not care about destroying the world anymore, and instead just wishes to reset the timeline, so everything unfolds again from the beginning.

He then says that his first form is just a fraction of his real power, and absorbs the SOUL of every monster in the Underground (except Napstablook) to transform into his final form. Asriel tells the protagonist that they will die in a world where no one remembers them. The protagonist calls the Lost Souls inside Asriel, and he tells them that the reason he keeps fighting to keep them around is because they are the only one that understands him and the only one who is fun to play with anymore.

After saving the protagonists friends, the protagonist realizes there is one person left to save. They call out to Asriel himself, breaking his confidence and ultimately destroying his will to fight.

Asriel begins crying and reverts to his original form. He then realizes that the protagonist was not the first human, and asks what their name is. The protagonist will respond "Frisk." He tells Frisk how many other monsters love them, and apologizes to Frisk for hurting them. He then proceeds to destroy the barrier that keeps the Underground apart from the surface and returns the monster SOULs to everyone.

He will then talk to Frisk more, telling them that he has to go. Frisk has the option of hugging Asriel to comfort him before he disappears, and Asriel will ask them to take care of his parents.

True Pacifist Ending
During the epilogue, he is seen at the flowerbed where Frisk fell at the beginning of the game. He tells about the first human, and how they were not the great person he thought they were. After his dialogue has been exhausted, he will simply ask if Frisk has anything better to do.

After the credits sequence, when reopening the game, Asriel returns as Flowey, begging the player not to reset the game, as that would erase all of Frisk and the monsters' happiness and progress. After reopening the game Asriel no longer appears in the epilogue or the credits sequence unless the player resets the game.

Genocide Route
After the protagonist kills Toriel, Flowey tells them that they are not really human, and mistakes them for the first child, telling them that they are still inseparable after all those years.

When the protagonist reaches New Home, Flowey tells the protagonist everything about his life as a flower, his shock when he woke up in the garden without limbs, his lack of feelings and compassion, his suicide, and how he got the ability to SAVE. Flowey explains that at first, he used his SAVE ability for good. After a while, however, everyone became predictable, and that is when he decided to kill others. Flowey dismisses his reason for killing people as an excuse, assuring the protagonist that they themselves know how liberating it is to act that way, and calling out those who "want to see it, but are too weak to do it themselves." He then says that even that bores him and that he has seen and done everything that can be done in the world. Flowey tells the protagonist how unique they are, and how their determination is greater than his. He tells them how tired he is of everything and how much he wants to show humanity that despite everything, this world is still kill-or-be-killed. He then realizes that the protagonist will not hesitate to murder him as well, and escapes to Asgore, warning him about the protagonist.

After the protagonist defeats Sans, they easily kill Asgore. Flowey destroys his father's soul and pledges himself to the protagonist one final time in an attempt to save his own life, revealing his true identity as Asriel in the process. He cries and begs the protagonist not to kill him, to no avail.

In Battle

 * See Asriel Dreemurr/In Battle

Player
Asriel speaks to the player directly when the game is re-opened after the True Pacifist Ending Credits while in his Flowey form, begging them never to play the game again, for the sake of everyone's happiness.

Frisk
In the beginning, Flowey attempts to kill Frisk and steal their soul, telling Frisk that it is a "kill or be killed" world.

In the Neutral Route, Photoshop Flowey fights Frisk and intends to kill them as many times as possible to make them suffer.

In the Pacifist Route, Asriel will mistake Frisk for the first human, and calls them his best friend. After the final boss fight, Asriel will realize that Frisk is not the First Human, and ask what their real name is. He will then later tell Frisk, if they find him, that he is grateful for them saving the underground and his family.

The First Human
Asriel was the first to find the first human when they fell into the Underground. He became Chara's best friend after helping them, and then the first human's brother after Toriel and Asgore adopted them.

Asriel plotted with the first human to absorb their SOUL and go to the surface and then collect six more human SOULs to break the barrier. Though Asriel backed out of this plan after bringing the first human's body to a flower patch in the village, stopping the first human's consciousness from taking over and killing the humans there. Even though the humans were hostile and ultimately mortally wounded him, he still walked back peacefully into the Underground carrying the first human's body.

In the Pacifist Route, he describes the first human as being the only one who understands him.

In the Genocide Route, Asriel describes their relationship as inseparable after a long time passed. At the end of the route, however, he becomes fearful of the first human, killing Asgore and destroying his SOUL before the first human could steal it and break out of the underground. After saying they are still best friends and begging the first human not to kill him, they will do so, stabbing him until there is nothing left.

However, Asriel does allude to the first human if the player reaches the Neutral Route a second time, as the only one whom he still feels that they understand him. However, Asriel then states that even then, he could not truly care about them.

Asgore
Asgore is Asriel's father. In different timelines, when Asriel woke up as Flowey, Asgore was the first to find him. Asriel informs Asgore of his identity, hoping to feel something and possibly turn back into his original form. However, he discovers he feels nothing for Asgore any longer, and grows to hate him.

Asriel then reloads into other timelines and murders Asgore as well as other monsters.

In later timelines, as well as the one where the player is in, Asgore does not know of Flowey.

Asriel's habit of saying "gosh," "golly", and "howdy" may come from Asgore.

Toriel
Toriel is Asriel's mother. In older timelines after failing to feel anything with Asgore, he had turned to Toriel in hopes of feeling love again with her. Though this ultimately failed as well and led to him resenting everyone in the Underground as well as his own parents.

In other timelines, after not feeling anything, he starts killing Toriel and the other monsters to try and feel something.

In the current timeline with the player, Toriel is unaware of the fact that Flowey is Asriel.

Alphys
Flowey is a byproduct of Alphys' experiments with determination.

The first seed that bloomed when Asriel returned after bringing the first human out of the Underground was also a seed that Asriel's dust remained on, trapping his essence inside of the flower once Alphys injected it with determination. (Essence and SOUL are different while SOUL is the monster's soul, the essence is only part of it, and is the remnants of a broken SOUL.)

It is not known if Asriel is aware of this or not, though it is possible he knows of the True Lab.

Sans
In one of the Neutral Endings, Flowey refers to Sans as "Papyrus's garbage brother" and "smiley trashbag" and holds a deep disdain for him. Apparently Sans "caused more than [his] fair share of resets", as if in some of Flowey's previous endeavors with his SAVE ability he was forced to engage Sans and was defeated by him.

Papyrus
Asriel as Flowey thinks of Papyrus as a fun person to mess around with, which he does before and during the events of Undertale. Papyrus has created a Flowey Fan Club several times. Flowey tells Papyrus about New Home at the end of the True Pacifist Route.

Name
Asriel's name is a combination of his parents' names, Asgore, and Toriel, likely stemming from Asgore being terrible at naming things.

Asriel's name has several possible meanings or origins. When attempting to name the Fallen Child "Asriel", the response becomes "..." and prevents the name from being used.
 * "Asriel" might be derived from "Azrael," the Angel of Death in Judaism and Islam. Gerson mentions an Angel of Death in his explanation of the Delta Rune prophecy.
 * "Asriel Dreemurr" is an anagram of Serial Murderer.
 * "Dreemurr" is similar in pronunciation to "Dreamer," alluded by the ACT "dream" in his battle, and his leitmotif "Hopes and Dreams."
 * "Asrieel" is also a name of Hebrew origin that means "Helped by god". This might be a reference to Asriel being miraculously saved and turned to flower after dying, or helping Frisk by breaking the barrier with his god-like powers.

Trivia

 * Both Undyne the Undying's armor and Mettaton NEO's body closely resemble Asriel's Angel of Death form, displaying a heart on the chest (and both gloves in Undyne's case), large, spiked shoulder pads, and, in Mettaton NEO's case, enormous, vibrant wings.
 * Napstablook is the only monster whose SOUL is not absorbed by Asriel.
 * If the game is hacked, it is possible to spare him during his boss fight, and the protagonist will be left on overworld where they left off: in front of Asgore, with the six souls. Nothing will happen, and the protagonist can walk around and even above the barrier.
 * It is possible that Asriel inherited his father's trait of being bad at coming up with names, as when he is in his flower form he names himself "Flowey".
 * If the letters in Asriel's full name, Asriel Dreemurr" are rearranged, they can form "Serial Murderer".