Backstory of Arthas:
Arthas Menethil is a Character from Warcraft III and World of Warcraft. Warcraft 3 takes place on the planet Azeroth, which was recently Invaded by the Orcish Horde in Warcraft 1 and 2. There are 4 main factions in Azeroth at the time of Warcraft 3. They are The Alliance, The Horde, The Kirin Tor, and the Scourge. Arthas's father, Terenas Menethil, is the leader of the Alliance until he was murdered by Arthas. After his death, Varian Wrynn, king of Stormwind, becomes leader of the Alliance. The Leader of the Horde is Ogrim Doomhammer, the leader of the Scourge is Arthas Menethil, and the Leader of the Kirin Tor is Antonidas.

Arthas Was a Paladin in his earlier years, but then the Scourge Invaded Eastern Kingdoms, The continent which all of the alliance cities were on, he struggled to maintain his standing as a Paladin. It all started when the Scourge Invaded of the cities ruled by Lordaeron (Lordaeron is the Capital of the Alliance Prior to Terenas's Death) called Stratholme. Arthas believed the best thing to do was to kill everyone in Stratholme, whether they were innocent or not did not matter. Arthas then led an army on Stratholme, slaughtering everyone in his path. He did not care whether they were young or old, man or woman, he killed everyone. In fact, at one point a little boy walked up to him and asked, "Prince Arthas! Are you here to save us?" The young boy had barely finished his sentence, and then Arthas killed him. He then turned to the boy's mother and killed her. Then further into the city, he was met by an undead army. Arthas's troops did not have the power to kill them. They retreated. Arthas then went to Northrend, another continent on Azeroth, and retrieved the legendary sword, Frostmourne. They returned to Stratholme, and with his new sword, Arthas destroyed the undead army. Arthas then returned home to Lordaeron. At the point of returning home, all the Holy light had been drained from the paladin, only to be filled with the Icy, Dark whispers of Frostmourne. When he returned to his father's throne room, Frostmourne told him to kill his father, and he did just that. He then runs out of the city, killing every citizen in his path, then raising them into undeath. He makes his way to the graveyard where his horse, Invincible was buried. Invincible was his friend since childhood, but when he was riding him one day, Invincible broke his leg, and then later died from his injury. But he was going to fix that. He raised his Horse from the dead, and then rode of into the distance. He made his way for Icecrown Citadel, in Northrend. there he found a old, rusted helmet frozen on a throne made of ice. He broke the helmet free from the ice. the Helmet Whispered to him in a low, Shrieking Voice. "Put me on..... Embrace the Frost.....Embrace Undeath.....". Arthas had nothing else to live for. He killed his father and His people. The screams of All of the Innocent people rang through his head. Arthas listened to the Helmet, He put it on. Arthas had become The Lich King, Commander of the Scourge.
Here is a link to the Warcraft 3 Frozen throne End cinematic and the part where he killed his father:
Arthas Kills Terenas: https://www.youtube.com/watch?v=vr7A19TPN_k
Icecrown Citadel: https://www.youtube.com/watch?v=vN5gUXFeRSQ

Arthas Menethil, Death Knight
Strength- 32
Intelligence- 24
Dexterity- 12
Charisma- 7

Abilities:
Raise Dead- Raises dead people as Zombies
Command Scourge- Commands the Massive Armies of the Scourge
Remorseless Winter- Drains Life from all enemies
Chains of Ice- Chains Enemies to the Ground with shackle made of Ice
Death Grip- Pulls and chokes Enemy
Disabilities:
Anything Living he touches starts to decay
Screams of all the innocent people he has ever killed echo through his head

Equipment:
  Frostmourne-
Frostmourne is a Two-Handed Longsword, and on the hilt the following is Inscribed:
“Whomsoever takes up this blade shall wield power eternal.
Just as the blade rends flesh, so must power scar the spirit.”
  Helm of Domination-
The Helm of Domination was Crafted by Ner'Zhul, who was an orc, as well
as the first Lich King. The helmet is what allows Arthas to command
the vast armies of the scourge.