Caster of Black

"It is comforting to feel emotions you expressed to me. However, I hate humans. I hate this world. Even staring with them eye to eye troubles me. That's why I wear a mask. Why would you believe that I don't have any attempt to disown you? [...] Adieu, Roche."

- Avicebron betraying and killing Roche

Caster of "Black" ("黒"のキャスター, "Kuro" no Kyasutā?), real name Avicebron, is a supporting antagonist in Fate/Apocrypha. He is the Caster-class Servant of Roche Frain Yggdmillennia of the Black Faction in the Great Holy Grail War. He also becomes the proxy Master of Berserker of Red after capturing him. In Fate/Grand Order, he is able to be summoned by Ritsuka Fujimaru in the Lostbelts.

He is voiced by Mitsuru Miyamoto in Japanese version and by Cam Clark in English version.

Historical Information
Avicebron, also known as Solomon ibn Gabirol, is a twelfth-century poet and philosopher. He was born in Malaga, Spain, and was the father of an entire thaumaturgical system, Kabbalah, and a starting point of the process leading up to the European Renaissance by bringing Greco-Arabic and Jewish lore and enlightenment to the cultural circles of Europe. He is recognized as a "hero" for his influence on world history and thaumaturgy.

He suffered from many illnesses during his life and spent his days with almost zero contact with other humans. He even purposefully created maid-type golems to take care of the housework in order to maintain his isolation.

In Fate/Apocrypha
Under his service of the Black Servant, Roche refers to Avicebron as teacher/master (先生, sensei?) out of respect. Caster is impressed with Roche's passion for golems, when he gave advice to Roche, he would immediately try to correct those points and aim to make them better. If Roche had existed in Caster's lifetime, Roche might have been able to serve as his pupil with his outstanding talent. Roche is similarly cynical, but the two have a good working relationship.

However, Caster is bad with children due to his poor health in his lifetime and never having any contact with children, and a situation where a child adored and idolized him like this was simply baffling and uncomfortable for him. Caster liked that there was a family lineage that still continued to pass on the mysteries of golem-making that he and his forefathers had created. Although Roche is an ideal Master for him, he seems to have plans of his own, noting that it is only ideal for the time being.

Eventually, Avicebron betrayed the Black Faction by joining Shirou Kotomine. He killed Roche by using him as a fuel to his Noble Phantasm. He was eventually killed by the combined force of Sieg and the Archer of Black.

In Fate/Grand Order
"I killed a human once, during the Great Holy Grail War. I did a truly repulsive crime. It's so disgusting that it shall leave an eternal scar on my saint graph, I suppose so."

- Avicebron showing remorse over betraying and killing Roche

In Fate/Grand Order, Avicebron became a Caster-Class playable Servant following the release of Anastasia: The Permafrost Empire. Here, he's exactly the reformed version of the Caster of Black from Fate/Apocrypha and had his original counterpart's memory.

Avicebron is summoned by Ritsuka Fujimaru in the "Anastasia" Lostbelt. Although his Saint Graph had not been aquired by Chaldea, the "cries of the land" themselves forced Avicebron to be summoned, as they were stronger than Ritsuka's bonds with their Servants. In this version, Avicebron shows a nicer, more capable and more loyal persoanality, playing an important role in the quest of Russia Lostbelt. After faking his betrayl in order to help Ritsuka against Kadoc Zemlupus, Avicebron sacrifices himself to power his Golem Keter Malkuth phantasm in order to allow Ritsuka to fight against the awakened Tsar Ivan the Terrible.

In the later Inheritance of Glory event, which is a crossover between Fate/Grand Order and Fate/Apocrypha, Avicebron serves as a supporting character alongside Sieg and every other Servants from both Red and Black Faction, with the exception of Shirou Kotomine. He constructs golems in the training and the assualt against the Hanging Garden of Babylon.

During his monologue unlocked after finishing the gameplay of Russia Lostbelt, Avicebron states that he tries to make amends out of remorse over betraying and murdering Roche.

Trivia

 * Due to his fully unchangable mask and motion, Avicebron has the least expression sheet among all of the Playable Servants in Fate/Grand Order, unlike other masked Servants who eventually took off their mask to show their face and expressions while talking.