Victor, also known as Luthor, is the boss of Victor's Fortress. Victor is the ex-leader of the Silver Knights, and the leader of the Black Knights. He served under Ascendant God and betrayed the Silver Knights for his own greed of power. Thanatos was actually using him for his own purposes.
Victor, in his second form, also appears throughout Silver Land's Boss Gates.
According to the description of Rama and his Monster Card, Victor was said to be "fleeing" from the Chase, and trying to use the Vajras to become one with Rama. However, the true Rama himself came along and punished Victor with death.
However, none of these are actually true from seen in-game. There was nothing about him trying to retreat, train, or even killed by Rama; it was Fighter instead. However, because Jin has Rama as his job it could be speculated that the true Rama killed Victor but not as the job.
King Fang informs Jin that the messenger who appealed to him had an aura similar to those of a Silver Knight, but the aura was like a dark fog rather than clear, bright energy. Jin concludes Victor betrayed Silver Land.
Victor is seen at his own castle, and he taunts Jin claiming he used and killed the Silver Knights as they were weak and Silver Land can only be protected with darkness. Jin vows revenge.
After defeating his first form (drops to 10% HP), he regains full health, and goes under a transformation (the Grand Chase call it "Revival").
After defeating his second, he seems to "revive" again. The battle almost seems endless and tiring, but Jin requests that the Chase believe in him. They do so, as Jin (Fighter) enters Burning Rage, and executes Burning Fist of 10,000 Hells, which kills Victor upon impact.
Upon Victor's defeat, he asks the Lord of Darkness for more strength, but one of his "Voices" tell him that Victor was just his pawn, and leaves him to die.