Asgore Dreemurr

"Human, it was nice to meet you. Goodbye."

- Asgore before he fights Frisk

Asgore Dreemurr is the king of the monsters of the Underground, Asriel's father, and Toriel's ex-husband. He serves as the false antagonist in the 2015 award winning indie game, Undertale.

Personality
Despite Asgore's threatening claims by the other monsters of the Underground to Frisk, Asgore is a kindhearted ruler who loves each and every one of the monsters that live in the Underground. Despite Asgore's claim to destroy humanity, he knows it may not be the right choice, as he does not want any of his warriors to risk being killed on the battlefield, especially Undyne. During the fight against Frisk, he conceals his face by looking downwards, showing his reluctance to fight back.

History
King Asgore and Queen Toriel ruled the Underground full of monsters for millennia after humans sealed the Underground with a barrier after the war. Toriel and Asgore later had a son, Asriel, and adopted the first human to fall into the Ruins.

Following the accident that led to their children's demise, Asgore, determined to avenge his children, swore to kill every following human who fell into the Underground and collect enough of their SOULs to shatter the barrier and destroy humanity. Toriel, disgusted by Asgore's lust for bloodshed, left him and returned to the ruins.

Before Frisk fell into the Underground, six more children fell into the Underground and died, with Asgore collecting their SOULs for future use.

Neutral Route
Asgore meets Frisk inside of his thrown room and offers to show them the barrier. He gives them a chance to turn back if they have anything left to do. Asgore does not mind the delay, admitting that he is not ready either.

As the fight begins, Asgore says it was nice knowing Frisk and destroys the player's Mercy option, forcing the player to use the Fight option to defeat Asgore.

Once Asgore is low on health, he admits defeat and lets Frisk be able to take his SOUL and exit the Underground. Frisk then can decide whether to kill or spare Asgore. If killed, Asgore turns to dust and reveals his SOUL with a smile on his face. If spared, Asgore is amazed that Frisk would remain in the Underground and promises that he and Toriel will take care of them as a happy family. However, regardless of Frisk's decision, Asgore's SOUL is shattered by Flowey, who takes the six souls from Asgore to transform into a God.

If the player spares Asgore on their second run through the Neutral Route after sparing him on the first, Asgore instead insists that the player to take his SOUL as he says it was what Asriel would have want, before finishing himself off.

True Pacifist Route
When combat with Asgore begins, it is interrupted by Toriel, who hits him just like how she hit Flowey at the beginning of the game. She tells Frisk and Asgore she interrupted their fight to prevent them killing each other to let either of them pass. Asgore is amazed to see her again, but she reminds him how she disliked his plan to collect the SOULs, plus he could've gone through the Barrier after collecting one soul, but instead chose to wait and hope another human never came. After that, Undyne, Alphys, Sans, and Papyrus join in the conversation, but it is all interrupted by Flowey, who absorbs all of their SOULs to transfer back into his original form, Asriel Dreemurr.

During the fight against Asriel, Asgore, alongside Toriel, appear as Lost Souls that Frisk must save to defeat Asriel. At the end, Asgore, alongside the rest of the main characters, venture outside the broken portal and witness the Sun setting from atop Mount Ebott. Asgore says that it will be the beginning of a new era, in which monsters and humans will live together at peace. He also asks Frisk to be the ambassador of the monsters. During the end credits, he is seen trimming a hedge into the face of Papyrus in front of Toriel's new monster school.

Genocide Route
When Frisk/Chara reaches the thrown room after killing Sans, Asgore, who was warned by Flowey of their arrival, doesn't recognize the protagonist as a human, asking them what kind of monster they are. Frisk/Chara initiates combat and instantly depletes Asgore's health bar with 9,999,999,999 damage without any player action. Flowey, showing his "loyal" side to the player, deals the final blow to Asgore and destroys his SOUL, although his plead for mercy is ignored and he too is mercilessly killed.

Trivia

 * His first name is an anagram of the Latin word "Aegros," which can mean troublesome, anxious, sad, difficult, or reluctant.
 * Asgore is immune to biologically aging until his child and successor has grown old enough to take his parents' position as the leader of the Underground. However, since Asriel is dead, Asgore is unable to age permanently, therefore immortal.
 * Asgore's voice can be heard in the Game Over screen and when the player sleeps in Toriel's home after sparing or killing her. These were his spoken lines to the first child on their deathbed.