Do all the characters' names have some kind of joke or meaning to them?

[Pian]

Toriel is short for tutoriel, Sans and Papyrus are named after fonts, and Undyne sort of sounds like undying. What about Alphys, Asgore, and Mettaton?

[Zaltys]

Originally posted by Demon Cat Lord:

what about alphys?

Might simply be scrambled sylph. Sylphs are elemental spirits of air, just like Undine are spirits of water.

...but that doesn't really fit Alphys. She's more like a Salamander (fire spirit). Since, you know, she's a lizard and lives in Hotlands.

[(Edgy) Asriel Dreemurr]

Mettaton
-Is a play on "met a ton" because he's famous.
-As well as the word "meta" which when used as a prefix means a change of some kind, or the aftermath of a change. As in Napstablook's cousin's change when becoming a robot. There's also a posibility that Mettaton was once female giving the character a sort of transgender message.

Asriel Dreemurr
-Is an angram of "serial murderer" as in Flowey .
-The combined names of Asgore and Toriel.
-Asriel is a modern spelling of Azrael which in some religions is the name for the archangel or angel of death. Asriel is also the "Angel of Death" in the prophecy described by Gerson.

Chara
-Is short for character, in order to fit the name length limit, and happens to be an actual name.

[LeBron]

Alphys name is Alphys because Toby Fox just liked the ♥♥♥♥♥♥♥ name.

[Starbright ✨]

Can't say whether it's coincidental or not, but Alphys' name anagrams to "shy pal."

[LeBron]

Originally posted by TheSteelFire:

Can't say whether it's coincidental or not, but Alphys' name anagrams to "shy pal."

Wow a necromancer, I would document this if Bill would let me.

[Zaltys]

Oh, that reminds me.
One of the anagrams for Undertale is Deltarune.

Remember what Gerson said about the emblem?

Eh? You don't know what that is?
What are they teaching you kids in school nowadays...? Wa ha ha!
That's the Delta Rune, the emblem of our kingdom.

[LittleBearAndChicken]

[SPOILERS OF COURSE]
Alphys:
Likes undyne a lot -> Undyne is a fish -> Alphys is all over that fish -> all fish -> allfish -> Alphys

Undyne:
She just doesn't want to die -> undying -> Undyne

Napstablook:
napster = music sharing software
Napstablook likes music a lot.
napster bloke -> Napstablook

Papyrus -> from the font papyrus
Sans -> from the font comic sans

Toriel -> she gives you the tutorial, get it? The tu-TORIEL

Asgore Dreemurr -> flip the letters around -> it's an anagram for "Sage or Murderer" -> because of the different ways you might view him when he tells his story before he dies.

Asriel Dreemurr -> anagram for Serial Murderer.

Mettaton -> Quoting this one from the wiki:
"Mettaton" is similar in pronunciation and spelling to "Metatron", the highest angel in Jewish lore, transliterated into greek as MTT. It could also be a portmanteau of "metal" and "automaton"

Chara -> she's a main character in the game, get it? CHARA-cter

[Zaltys]

Originally posted by Jari-SoftwareEngineer-Kun-Chan:

Chara -> she's a main character in the game, get it? CHARA-cter

Hebrew: חָרָה, Charah, to burn with rage.

Before you say that's farfetched, lemme point out that Asriel is also a Hebrew name.

Originally posted by Jari-SoftwareEngineer-Kun-Chan:

Napstablook:
napster = music sharing software
Napstablook likes music a lot.
napster bloke -> Napstablook

Also the first encounter: 'naps to block'.

Mettaton -> Quoting this one from the wiki:
"Mettaton" is similar in pronunciation and spelling to "Metatron", the highest angel in Jewish lore, transliterated into greek as MTT. It could also be a portmanteau of "metal" and "automaton"

It's also commonly spelled as Mattatron (also in Hebrew), which is even closer. By the way, the Megaten series portrayed Metatron as a metallic android angel: http://vignette1.wikia.nocookie.net/megamitensei/images/9/9c/MetatronSMT2.jpg

[Blessed Evelyn]

Originally posted by Zaltys:

Originally posted by Jari-SoftwareEngineer-Kun-Chan:

Chara -> she's a main character in the game, get it? CHARA-cter

Hebrew: חָרָה, Charah, to burn with rage.

Before you say that's farfetched, lemme point out that Asriel is also a Hebrew name.

Originally posted by Jari-SoftwareEngineer-Kun-Chan:

Napstablook:
napster = music sharing software
Napstablook likes music a lot.
napster bloke -> Napstablook

Also the first encounter: 'naps to block'.

https://youtu.be/_F-2k_23yaA

[JackofCookieJars]

I'm gonna necro post, but I was having a random tangent thought train that led me to the thought "Alphys sounds kinda like physicist, and if there's reason behind that, then where's the Al part come from." Which made me think of another type of modern science chemistry, which is based on the word Alchemist which reminded me that Alchemists chased down a way to turn metals into gold THROUGH MAGIC, often becoming royal aides or something. Alphys, the royal scientist, dabbled in both MAGIC (her determination metaphysics experiment) and modern day science (modifying Frisk's cellphone).

Jeez, putting it that way makes me think I was making an illuminati theory.

[Entropie]

Originally posted by Toilet:

Very interesting interpretations, thanks for sharing. Is there any other meaning to Undyne's name. I was thinking because she's a fish and "un"+"dyne/dine"=not dine, her name is telling us not to eat her. Also, what would Alphys be an alpha of, she seems like a very shy and submissive girl.

Undine is also a word describing an elemental spirit of water.
Thus in rpgs I usually think of something like that when that name pops up.
(Secret of Mana for instance features an Undine)

[CrowFoxy]

Originally posted by Talby:

I thought of Metatron when I met Mettaton, but it might also be a pun. He's so popular because he's Mettaton of people.

LOL

[Pixelucifer]

Originally posted by Toilet:

Toriel is short for tutoriel, Sans and Papyrus are named after fonts, and Undyne sort of sounds like undying. What about Alphys, Asgore, and Mettaton?

METTATON.
Met a ton.
Met a ton of fans.
nyuknyuknyuk

[(Edgy) Asriel Dreemurr]

Originally posted by (Edgy) Asriel Dreemurr:

Mettaton
-Is a play on "met a ton" because he's famous.
-As well as the word "meta" which when used as a prefix means a change of some kind, or the aftermath of a change. As in Napstablook's cousin's change when becoming a robot. There's also a posibility that Mettaton was once female giving the character a sort of transgender message.

Asriel Dreemurr
-Is an angram of "serial murderer" as in Flowey .
-The combined names of Asgore and Toriel.
-Asriel is a modern spelling of Azrael which in some religions is the name for the archangel or angel of death. Asriel is also the "Angel of Death" in the prophecy described by Gerson.

Chara
-Is short for character, in order to fit the name length limit, and happens to be an actual name.

Some more:

Toriel
-Is a pun on Tutorial, as stated by the OP

Undyne
-Play on undying since she's the only monster shown to have determination and come back at one point
-Based on Undines which are water elemental spirits in the teachings of alchemy, usually portrayed as guardians

Alphys
-An anagram of "a Sylph" and has the appearance of a "salamander", these being the elemental spirits of air and fire repsectively under the same teachings of alchemy in Undyne's case.

Sans
-Based on the font name "comic sans" due to his comedic nature, and later find out that he is in fact a practicing comedian
-Comic sans is usually seen as a goofy unprofessional looking font, which coincides with Sans's outward character traits, but those that have performed genocide know his true nature which is anything but that.
-Based on J.N. Wiedle's webcomic Helvetica, which features an all-skeleton cast of characters, and the main character Helvetica is also named after a font.

Papyrus
-Based on the font name "papyrus".
-According to the internet, papyrus is a font that "looks cool, but isn't" it looks both goofy but also usable at the same time, this coincides with the character's attempts to become popular. He is cool, but just in his own wacky way.
-Based on J.N. Wiedle's webcomic Helvetica, which features an all-skeleton cast of characters, and the main character Helvetica is also named after a font.

[cloudy]

Whut about temmie? is there some hidden secret behind temmie flakes and paying tem to go 2 colege for 1000g?(i dont play undertale, i saw this on youtube)