Weaver's Servant who actually is Alexander(Iskander) the Great himself, the King of Conquerors. One of the most powerful servants in the War.
In his past life, Rider was Alexander the Great, the Macedonian king who almost succeeded in conquering the known world. Since encountering a friend with similar personality as Taiga Fujimura, Alexander developed a fascination with wanting to expand his horizons and explore the known world. Upon gaining the throne to Macedonia, Alexander waged a campaign of conquering neighboring nations and sought to expand his country's influence to as far as the end of the world. While conquering many lands throughout Eurasia, Alexander died young and his empire would collapse from warring factions within his kingdom dividing up the empire into separate territories.
Rider was created as a character for Gen Urobuchi's Fate/Zero light novel series. Aspects to his character were among the more difficult parts to develop for the novel, in particular the chariot he would ride into battle. It was originally going to have the ability to adjust its size by substituting parts as it got smaller and transformed, but this idea was scrapped as it would have only further complicated Rider's design during development. For the anime adaptation of Fate/Zero, Rider was voiced by Ohtsuka Akio in Japanese and Jamieson Price in English.
Rider stands at 212 centimeters tall (barely over 7 feet), having red hair and eyes with a long red beard for facial hair. He is a muscular man who normally wears bronze armor and a large, luxuriously decorated mantle into battle. For normal clothes, Rider wears an extra-large T-shirt and a pair of large jeans. The T-shirt has a logo of a video game called "The Admiral's Great Tactics", which Rider would play during his spare time while participating in the Holy Grail War.
Rider has a noble and overbearing personality, often willing to act according to his impulses. While seeming greedy and inconsiderate toward others with his personality, Rider strongly values any bonds he is able to establish with those he encounters and is willing to try understanding others at a personal level. Learning that the world was far bigger than he imagined during his time alive led Rider to have the desire of wanting to conquer the world as a human through wishing upon the Holy Grail. While having a love for battles and destruction, Rider tries to keep bloodshed to a minimum while in battle as his conquering involves more of earning the admiration of others instead of any material wealth.
Rider was summoned as a Servant by Waver to participate in the 4th Holy Grail War using a mantle once worn by Alexander the Great that Waver stole from his instructor Kayneth to prove his worth as a magi. His overbearing personality often clashed with Waver's timid persona, yet the two would gradually develop a close bond throughout the length of the Grail War.
Rider would arrange a King's Meeting with Saber and Gilgamesh at the Einzbern Castle to discuss their desires with the Holy Grail where he would become disappointed with Saber's desires and beliefs over ruling Britain. During the meeting, he would wipe out the remaining personalities of Assassin that arrived at the castle using Ionioi Hetairoi. Rider would also assist Saber and Lancer in trying to halt the threat that came to Fuyuki from the monstrous abomination summoned up by Caster.
Before his final battle against Gilgamesh, Rider would lose his Gordius Wheel in an encounter with Saber when she used Excalibur on it. When fighting Gilgamesh, he offered an alliance with the King of Heroes to conquer the world which Gilgamesh turned down. In their fight, Rider would be slain through Gilgamesh's use of Ea. As a show of respect towards his foe as Rider vanished, Gilgamesh offered the King of Conquerors the opportunity to fight him again at any time he desired and would honor his request to spare the life of Waver.
While in battle, Rider would make use of two Noble Phantasms: Gordius Wheel and Ionioi Hetairoi. The Gordius Wheel is a chariot pulled by a pair of divine bulls that are capable of trampling over any foe they charge towards while engulfed in lightning. Ionioi Hetairoi is Rider's Reality Marble where he pulls his foes into a vast desert to be attacked by a large army of soldiers led by Rider, each of whom also being a Heroic Spirit. Rider leads his armies while riding his horse, Bucephalus, and is able to summon the horse or any of his soldiers outside of the Reality Marble for a limited amount of time depending on his mana reserves.
While preferring to fight on a mount, Rider can also fight on foot as he makes use of a spatha called the Sword of the Kupriotes to attack his foes. While not a Noble Phantasm, the sword is still an effective weapon in combat as it is sturdy enough to deflect thrown dirks tossed by Assassins and it is used by Rider to summon up his Noble Phantasms. Though able to fight on foot, Rider does have a low Agility rating that would make it difficult for him to evade attacks from faster foes if he lacks a mount to ride on.