Rezo the Red Priest (Japanese: 赤法師 レゾ Romaji: aka hōshi rezo) is one of the "Five Great Sages", a world-famous priest and healer from the Slayers series. His Japanese voice actor is 子安武人 Takehito Koyasu and his English voice actors are Charles Rolfe in episodes 3-10 of Slayers, Peter Davis in a flashback during episode 23, and Liam O'Brien in Slayers REVOLUTION and Slayers EVOLUTION-R.
It is never said exactly how old Rezo is, but according to Zelgadiss, he is over a century old. However, he does not look his age (in the first novel, Lina describes him as looking "both young and old at the same time"). Rezo's only known relative is Zelgadiss Graywords, who is either his grandson or great-grandson (the rumor that Rezo was both his grandfather and great-grandfather was the result of a translation error in the English dub).
Rezo was born with one of the seven pieces of Ruby Eye Shabranigdu sealed within his soul, which somehow affected his eyes, and he was blind as a result. He also possessed an immense capacity for magic, and took up studying white magic in an effort to cure his blindness, not realizing what the true cause of his blindness was. Once he mastered white magic, he traveled the land healing the sick and blind, performing "miracles." Sadly, although he was able to cure the blindness of others, he could not cure his own. Thus he studied shamanistic magic and black magic, hoping in vain that one of the two fields might provide him with a cure.
At some point, Rezo visited the kingdom of Taforashia. While there, He decided to create the Durum sickness. Rezo sealed the bodies of all the inhabitants in crystal vats until a cure could be found. In reality, however, his ultimate goal was to use the sealed bodies as test subjects for soul transfering with the Hellmaster 's Jar in an attemp to regain his sight. He also transferred the prince of Taforashia and his good friend Duclis' souls to their current beast forms so that they could search for a cure without being affected by the disease, as their original bodies had already caught it. Rezo also used them secretly to see if the Hellmaster jar actualy worked
Slowly Rezo's desire to find a cure turned into an obsession, and the fragment of Shabranigdu within him began to corrupt his soul and take over. Rezo eventually decided that resurrecting Shabranigdu was the only way to cure his blindness. He hoped that in exchange for reviving him, the ma-ō would grant him sight. In the anime, however he believed that the fragment was sealed within his tower, not within himself.
Originally, Rezo intended on defeating Shabranigdu once he had gained his sight, and so he began to research methods of fighting the dark lord, summoning the mazoku Tība to help him. Eventually he created a stone tablet from the Claire Bible, although he never got a chance to use it.
Afterwards, he began searching for the Philosopher's Stone, believing that it was the key to the Dark Lord's revival. He eventually obtained the stone, and resurrected Shabranigdu from within himself. In the end, Lina Inverse was able to defeat the dark lord using the Giga Slave and the Sword of Light, with help from Rezo's soul. After the fragment was destroyed, before Rezo passed into heaven, his final words were: "Please forgive friends. I'm sorry, and thank you".
Rezo's most important companion was Eris Vrumugun, his assistant who helped him do research, experiment, and perform his miracles.
Eris also helped create Rezo's clone, which he used to practice sorcery on in an effort to help cure his blindness. This clone was known as Copy Rezo, who grew to hate the original Rezo.
Exactly how Rezo felt about Zelgadiss is a little ambiguous. Although he turned Zelgadiss into a chimera, it has been speculated by Lina that it was the fragment of Shabranigdu sealed within him that was actually responsible. Regardless of whichever possibility may be true, Rezo completely alienated Zelgadiss as a result, causing him to turn against and betray the Red Priest.
Rezo also seems to have created Ozel, an artificial human maid of Gioconda, for the purpose of guarding his soul jar. She is very protective of it, and displays a great deal of affection towards the Red Priest.
In a fan-interview, Hajime Kanzaka has hinted at that Zelgadiss' parents were somewhat worried about what Rezo might do to their son, so the Red Priest killed them, disguising it as an accident. Zelgadiss may or may not be aware of this.
Although it has never been mentioned in any of the Slayers-related media, Rezo's surnamed was revealed by Takashi Watanabe, the TV series chief director, to be Graywords. Later this information was confirmed by the very same author, Hajime Kanzaka, in one of his multiple interviews with his official fan club.
Several incorrect assumptions were made by Lina in the first novel when she tried to reconstruct the events which led to the resurrection of Shabranigdu. She theorized that the ma-ō was sealed into Rezo's eyes, (thus making his blindness incurable,) and when Shabranigdu took control of the priest's body, Rezo's soul was slowly consumed by the mazoku, the part helping them at the end being the last vestiges of his essence. Later, when she fought against the fragment sealed within Luke, her theory proved to be incorrect entirely; she learned that the ma-ō was sealed into the souls of humans, and when a part of it is awakened, the two souls co-exist in the same body.
In Slayers Evolution-R, Lina seems to understand that Shabranigdu was not sealed in Rezo's eyes but in his soul, meaning that when Rezo was resurrected, Shabranigdu was in effect also resurrected. Interestingly, despite the fact that Shabranigdu is not sealed in Rezo's eyes themselves, it is shown that Rezo's vision acts as some sort of seal to prevent Shabranigdu from being released from his body. He refused to open his eyes when inhabiting Pokota's body, which otherwise should've allowed him to see easily, and he didn't dare open them until he requested for Lina to kill him.
- Slayers REVOLUTION (EP05 (appears in a flashback), EP09 (mentioned only), EP10-EP11 (appears in flashbacks), EP13 (mentioned only))