Rider (Fate/Advent ~ Manco Cápac)

Rider (ライダー, Raidā) is the main serving under ???. Normally boasting immense power, Rider's summon was compromised due to the summoning system used by ???, at the time, was still in its testing stages, which resulted in him being weakened exponentially. Rider is an Avatar of the Sun, which is also known as the Incan Sun God. Despite Inti's contradictory reasoning, he still wishes to assist the and prevent its destruction.

Rider is one of the main protagonists of Fate/Advent, belonging to ???, an organization whose purpose is to stop the ???, as well as returning timelines that have been wrongfully destroyed by them.

Identity
Rider's True Name is (マンコカパック, Manko Kapakku), the founder of the Incan civilization, known as the  at the time, within the Valley of Cusco, which predated the Incan Empire that was later found by the ninth Sapa Inca,. Within history, he was said to be the son of Inti, the Sun God of the Incas. However, this was later revealed to be incorrect by Rider himself, stating that he was never the son of Inti, but rather an avatar of Inti, who sent himself in the form of Manco Cápac onto the world to bring about the birth of the concept of civilization. Via the usage of the Tapac Yauri, Manco Cápac plunged it onto the ground, claiming that this will be the beginning of the Incas, which were subsequently founded then and there.

Despite the various legends surrounding Manco Cápac, there seems to be a lack of proof that he was a true historical figure. However, it is believed by the Incas that due to him, the Incas were able to exist. The theme of the Sapa Incas being deemed the Son of Inti began with him, and continued onward until the Incas were converted to Catholicism when the Spanish Conquistadors invaded and wiped out the majority of the civilization. It is because of this belief that all of the Sapa Incas are deemed to be Fire and Sun Gods by the Incan people.

Solar Nexus
Solar Nexus (ソーラーネクサス, Sōrā Nekusasu) is a Skill that cements the idea that Manco Capac is but a fraction of the Sun itself. This Skill essentially ties the Saint Graph of him to Inti, the Sun, receiving differing benefits from it. Due to the issues regarding his initial summoning, Rider solely possessed this Skill, which resulted in its extraordinarily low ranking.

Originally, Rider was known to be the Sun God Inti. However, after overseeing the humans, showing displeasure in how they functioned, Inti split from himself, resulting in the creation of Manco Cápac, the first Sapa Inca, and then sent him off to the World. Despite being split off from Inti, Rider is still tied to the Sun itself, feeding off of the Sun's own powers and resources for himself. This connection is primarily done via a series of Magical Paths tied between Rider and Inti. Due to this connection, Rider is constantly receiving Mana from Inti, regardless if the Sun's light is present or not. However, Rider does gain a larger amount of Mana from the Sun if the Sun's lights are able to touch his body.

The Sun is seen as a celestial body that helps planets thrive, as well as keep them in place. Without it, life on planets, if any, would continue to decline until nothing existed. This Skill enhances this relationship to extreme amounts, but Rider, at the time, only possessed the passive ability to receive Mana from the Sun, due to holding it an E in ranking.

Trivia

 * Rider uses the design of Yuri from the manga series Mahou? Sonna Koto yori Kinniku da!
 * Credit to the Type Moon Wikia for all of the material used from it.