Diablo

'"Your name shall be Diablo. Receive that name, and become my guardian deity!" '

- Rimuru naming the Arch Demon as Diablo upon Rimuru's awakening as a True Demon Lord.

Diablo is the named Arch Demon faithful servant of Rimuru Tempest. After being named, he has evolved into a Demon Duke and is currently one of the most powerful people in Tempest.

He is the leader of Black Corps.

Appearance
As an Arch Demon, he was a beauty whose gender was indeterminable. He possess crimson hair while his eye have golden irises and black sclera. Appears to be elegantly dressed in a professional butler uniform and carries himself with an air of dignity.

Personality
As a summoned demon who has been given a name by Rimuru, he is extremely loyal to his master. When two of his subordinates were sacrificed to fuel Rimuru's revival spell, he felt envious that they could be of use to his master. His aim is to be Rimuru's right hand man.

Aside from treating his master humbly, he often speaks politely to both his allies as well as enemies.

Birth of a Demon Lord Arc
By offering the corpses of the Blood Shadows and the 15,000 human soldiers, Rimuru summoned an Archdemon and his two greater demon subordinates. Using the corpses they were successfully able to materialize. He ordered them to capture the the three escaping Blood Shadows, and bring them to Ranga.

When the secret revival art was lacking the necessary energy, the Archdemon offered his two subordinates, stating that they were delighted to be of use to Rimuru. Hence, when Rimuru awaked he was grateful and allowed the Archdemon to become one of his comrades. When Rimuru found out the Arch Demon didn’t have a name, he named him "Diablo", tasking him to become his guardian deity. After Diablo was named, a black cocoon enveloped his body, creating a perfect evolution posture.

Saint Demon Confrontation Arc
"I am not an Arch demon like you had previously said, but a Demon Duke." - He reveals so while battling a Templar Knight.

It is later revealed that he is in fact not a Archdemon, but a Demon Duke. A Demon Duke is a legendary existence. It is supposedly ranked higher than a self-proclaimed Demon Lord. There has been no other Demon Duke summonings previously documented.

Magic

 * Magic Energy Manipulation Archive
 * High Demon Summoning

Unique Skills

 * Great Wiseman: Thought Acceleration, Thought Domination, Incantation Void.
 * Tempter: Fascination, Seduction.

Extra Skills

 * Multiple Barriers
 * Spatial Travel

Daily Skills

 * Magic Perception
 * Demon Lord’s Ambition

Battle Skills

 * Law Manipulation

Resistances

 * Physical Attack Nullification
 * Natural Effect Nullification
 * Status Change Nullification
 * Spirit Attack Resistance
 * Holy Magic Attack Resistancel

Relationships

 * Rimuru Tempest: He is truly loyal to Rimuru, and will spread calamity if ordered.

Trivia

 * He have red hair color in the Web Novel and black in the Light Novel.